User’s manual to Tuesday’s Senate elections

With the nonstop coverage of the presidential race, it's easy to forget that dozens of candidates are locked in heated battles for the Senate, which taken together could decide the balance of power in Congress.

Here's everything you wanted (or didn't want) to know about the Senate contests Tuesday.

Thirty three seats are up this cycle, with Democrats (and independents that caucus with Democrats) holding 23. Republicans have 10.

The chamber right now has 47 Republicans and 53 Democrats (including the two independents.) That means Republicans have to pick up four seats to take the majority if President Obama is reelected, just three if Mitt. Romney is elected. (In the event of a 50-50 split the vice president has the tie-breaking vote. And that scenario is well within the realm of possibility at this point.

Now off to the races ... starting with seats mostly likely to switch parties.

MAINE: Independent candidate Angus King looks poised to take the seat held by retiring Republican Sen. Olympia Snowe. So far King hasn't said which party he would caucus with in Washington. But given that the National Republican Senatorial Committee and party-affiliated groups have spent money attacking him and the Democratic Senatorial Campaign Committee spent money attacking his Republican opponent, the safe money is probably on King going with the Democrats. Oh, and in debates he has offered praise for ObamaCare, which is probably another tell.

MASSACHUSSETS: If this were a midterm election, the Bay State might not be this high on the list. Incumbent Republican Scott Brown has done just about everything right and had Democrat Elizabeth Warren on the ropes after a controversy over her alleged Native American ancestry. However, Warren has managed to pull ahead by nationalizing the race. In deep blue Massachusetts, in a presidential election year, that's a recipe for success. Even if Brown loses on Tuesday, his career in politics isn't over by a long shot. He is popular in his home state and voters there have been willing to vote for Republican governors (Mitt Romney, William Weld) in the past. Or if Obama is reelected, perhaps John Kerry moves down Constitution Ave to be Secretary of State. That would set up a special election to fill the seat, and Scott Brown is a solid special election candidate.

NEBRASKA: Republican Deb Fischer looks poised to defeat former Democratic Sen. Bob Kerrey to win the open seat in Nebraska. However, this race has been tightening in the last month. Kerrey has strung together a series of high profile endorsements - including former Clinton senior staffer Erskine Bowles, former Wyoming Republican Sen. Alan Simpson, former Nebraska Republican Sen. Chuck Hagel, and former New Hampshire Republican Sen. Warren Rudman. And he has hit Fischer with a barrage of negative ads to make it a close race. In the end though, this is a red state and it is a presidential year, which puts a heavy thumb on the scale for Fischer.

NORTH DAKOTA: Democrat Heidi Heitkamp appears to be the more likeable candidate and to have run a fantastic campaign. Republican Rick Berg can come off as brusque and hasn't hit the trail as well as Heitkamp. Still, he holds the advantage in deep red North Dakota.

INDIANA: This was a race that didn't have to be this close. Despite winning in 2008, the Obama campaign gave up on Indiana a long time ago. Republican Sen. Richard Lugar was unopposed in 2006, and probably would have been unbeatable in November. However, State Treasurer Richard Mourdock pulled a flanking maneuver to Lugar's right and won the Republican nomination. That left Lugar sore and unwilling to actively campaign for Mourdock, which may have hurt Mourdock with independents and moderate Republicans. The race was close, and a comment from Mourdock explaining his pro-life stance even in cases of rape dealt a crushing blow to his independent voter support. A late Indiana poll had Democratic US Rep Joe Donnelly leading the race by 11 percentage points.

MONTANA: Both candidates hold day jobs on Capitol Hill with essentially polar-opposite voting records. The wild card in the race between incumbent Democrat Rep. Jon Tester and Republican Rep. Denny Rehbert could be the impact of the Farm Bill to a largely agricultural state. It passed with bipartisan support in the Senate, but failed to even get a vote in the House. Could voters punish Rehberg for his chamber's inaction? We'll find out on Election Day.

Tester has shown an ability to keep the race close, but the fact that this is a presidential election year hurts his chances. The state is sure to go for Romney this time, and polls have consistently shown Rehberg with a narrow lead. It's Rehberg's race to lose.

WISCONSIN: Democrats and Republicans in the Badger State have been locked in seemingly non-stop combat since 2010. Republicans have come out the victors as of late in what was formerly a solid blue state.

Each side has its get-out-the-vote ground game down to a science. Will Republican Tommy Thompson get a bump from the presidential race with native son Rep Paul Ryan on the ticket as the vice president? Or will the Obama machine help Democrat Tammy Baldwin get a majority?

Polls have been up and down with a slight advantage to Democrat Tammy Baldwin for the open seat of retiring Democratic Sen. Herb Kohl. But this race will come down to the wire. If the presidential race is within one or two percentage points, that's good news for Thompson. If Obama is able to win by 3 percentage points or more that probably means Baldwin is your winner.

The outcome of the next three races depends heavily on voter turnout at the presidential level.

NEVADA: Republican Sen. Dean Heller has consistently led in polls throughout the contest. Democratic challenger Rep. Shelley Berkley has been plagued by a congressional ethics investigation. The wild card here is the Harry Reid Nevada Turnout Machine. Clark County (home to Las Vegas) is probably in the bag for Democrats, but it's unclear whether they can get enough votes in swing Washoe County to win. Berkley has run behind the president and will probably need him to carry the state by 5 to 6 percentage points to pull off the upset.

VIRGINIA: The Old Dominion promises to be a critical state in the presidential election. Democrat Tim Kaine and Republican George Allen, are former governors and seasoned political hands.

Allen has been hammering Kaine over his support for the Washington budget deal that led to the sequester, which would hit defense-heavy Virginia hard. Kaine is trying to tie Allen to the Ryan budget plan, which Kaine says would turn Medicare into a voucher program. This one will likely be based on presidential coattails. If Romney wins, this could be a key GOP pickup. If not, it may be a Democratic hold.

OHIO: Ohio is at the center of the presidential race, and while the Senate contest isn't as close, anything can happen. Democratic Sen. Sherrod Brown is to the left of his state's electorate, but his political skills, strong support of the auto bailout and toughness on China have put him in front. Republican State Treasurer Josh Mandel has a strong resume, but his opposition to the auto bailout and general aloofness has hurt his chances. Still, if Romney wins Ohio, there's a good chance it goes for Mandel as well.

ARIZONA: While he may be the perfect candidate for deep red Arizona, Democrat Richard Carmona still has a steep hill to climb if he wants to become the first Democrat to serve the state since 1995. Democrats have released internal polls that show Carmona in the lead, but public polling has consistently shown Republican Rep. Jeff Flake in front. Given the presidential contest, Flake will probably have the turnout advantage and heads into Tuesday as the favorite. However, both parties have spent millions in a state that looked to be safe at the beginning of the cycle.

MISSOURI: Democratic Sen. Claire McCaskill seemed bound for defeat because of Obama's unpopularity. Her travel reimbursements for flights on her husband's private plane seemed to seal her fate. But Rep. Todd Akin, a narrow primary victor in a crowded Republican field, told a local TV host in August that women had biological defenses against pregnancy in cases of "legitimate rape."

Akin apologized and recanted but lost the backing of the national party. Republicans said he was preferable, but withdrew financial support. McCaskill goes into the election as the favorite, though polls have tightened since August.

PENNSYLVANIA: While this was originally thought to be a sure hold for Democrats, Republican businessman and political neophyte Tom Smith has run an aggressive campaign and has an outside shot at pulling off the upset of the cycle. He's spent almost $16.5 million of his own money to date on the contest. However, Smith also has a solid base of support, out raising Democratic Sen. Robert Casey in the third quarter.

Some Democrats have worried that the incumbent Casey hasn't been taking his competition seriously enough and criticized him for keeping a light campaign schedule. Casey still has a slight edge given the political makeup of the state though.

CONNECTICUT: Former World Wrestling Entertainment President and CEO Linda McMahon is in the arena once again after getting a SmackDown!TM by Democrat Richard Blumenthal in 2010.

Her opponent this time, Democratic Rep. Chris Murphy, doesn't have the name recognition or resume of Blumenthal, but has the advantage of running in a blue state in a presidential year. McMahon has spent heavily in this race and in general has run a much better campaign this time but remains the underdog.

FLORIDA: Incumbent Sen. Bill Nelson, a Democrat, made his reelect all about his opponent Republican Rep. Connie Mack. Nelson early in the race defined and destroyed Mack. And the scion of a famous Florida political family hasn't recovered. Nelson has led the race since the beginning and looks to be the favorite Tuesday, despite millions in attack ads against him.

NEW MEXICO: Republicans recruited who appeared to be the right candidate in former Rep. Heather Wilson but she just hasn't gained traction. That coupled with the fact that the state should go for Obama at the presidential level bodes well for Democratic candidate Rep. Martin Heinrich for the seat of outgoing Democratic Sen. Jeff Bingaman.

NEW JERSEY: Daily Caller sex story aside, Dem Sen. Robert Menendez remains the heavy favorite in the Garden State. Republican Joe Kyrillos looked like he had a chance before Menendez started campaigning, but that is likely gone now.

MICHIGAN: Many felt that Democratic Sen. Debbie Stabenow was vulnerable given her low approval ratings at the beginning of the cycle. Former Republican Rep. Pete Hoekstra had a late surge to take the Republican nomination. However, many observers felt that a television spot he ran during the Super Bowl featuring an Asian actress facetiously applauding Sen. Stabenow in Pidgin English was racially insensitive and may have hurt him with general election voters. Stabenow has been the heavy favorite since the beginning.

HAWAII: Former Republican Gov. Linda Lingle faces off against Democratic Rep. Mazie Hirono in  rematch of the state's 2002 governor's race. Lingle is a good candidate but doesn't stand a chance in a year in which Hawaiian native Barack Obama is at the top of the ticket.

WEST VIRGINIA: Two Senate elections. Two ads feature Democratic incumbent Sen. Joe Manchin holding a rifle. Manchin will defeat Republican John Raese again and get a full term in the Senate. The tougher climber for Democrats appears to be 2014, when senior Democratic Sen. Jay Rockefeller is up for reelection.

The other states are not competitive: California, Delaware, Minnesota, New York, Rhode Island and Vermont for Democrats. Mississippi, Tennessee, Texas, Utah and Wyoming for Republicans.