Congress returns for its midsummer session Monday with a Senate supermajority not super enough for President Obama's top priorities to pass without Republican support.

The seating of Minnesota Sen. Al Franken will give Democrats the filibuster-proof 60-40 majority in the Senate, but only on paper. Absences by two ailing senators mean the party can count only 58 votes, and then only if Majority Leader Harry Reid can herd two independents and the independent streaks of 55 others behind Obama's biggest initiatives: expanded health care coverage and cleaner but more expensive energy.

Republicans are well aware that the closer the Democrats get to 60, the more leverage GOP senators have as Congress struggles with those problems that have eluded solutions for decades.

"With their supermajority, the era of excuses and finger-pointing is now over," said GOP Sen. John Cornyn of Texas, who heads the National Senatorial Republican Committee.

It's a fragile supermajority because Sens. Robert Byrd of West Virginia and Edward Kennedy of Massachusetts are ill and have not voted in weeks. It's unclear when or whether they might return to the Capitol.

Ill senators have voted by gurney and wheelchair in the past. But Democrats and Republicans said they don't foresee any votes in the coming week that would be close enough to warrant a trip to the Senate by either Byrd or Kennedy.

Byrd, 91, returned home this past week from a six-week hospital stay after a series of infections. Kennedy, 77, is battling brain cancer.

It's also a truism that it's often easier to get 80 votes and more than it is to get 60. Overwhelming support for legislation can become a persuasive force of its own. But if there's a chance of stopping or slowing a bill, other considerations factor in to a senator's calculus -- typically regional matters, ideology and plain self-interest as much as party loyalty.

Thus, Obama, Reid and Co. have much legislative horse-trading ahead of them on an assortment of items poised for consideration before Congress' monthlong August break.

Slowing it all down will be Senate hearings and debate on appeals court judge Sonia Sotomayor's fitness for the Supreme Court. Senate Judiciary Committee hearings are set to begin July 13, followed by what's expected to be a robust two weeks of committee and floor debate.

Democrats want her confirmed before Congress leaves for its summer vacation. Republicans have complained that her nomination is moving too fast. But they have struggled to raise public opposition to her confirmation without alienating Hispanics, the fastest-growing demographic and increasing powerful voting bloc.

On policy, Democrats in the House and Senate are pushing to begin votes by month's end on health care, the main work of Kennedy's public life. Obama has urged Congress to finish work by the end of the year on the bills designed control health costs and make coverage available to about 47 million people who lack it.

Kennedy's health committee, led in his absence by Sen. Chris Dodd of Connecticut, could meet as soon as the coming week to complete its version of the bill, which Obama has said reflects many of his goals. That includes a government health insurance option to compete with private plans.

At the same time, the Senate Finance Committee chaired by Montana Sen. Max Baucus is drafting a companion measure aimed at winning a bipartisan compromise. The government-run option for coverage is unlikely to be included in that version.

Senate committees also are set to tackle and energy bill that aims to reduce greenhouse gases blamed for global warming. Here, too, deep regional divisions among Democrats undermine prospects of nailing down 60 votes in favor of it.

House passage of the climate change bill on a 219-212 vote last month provided an instructional preview of the Senate debate. Speaker Nancy Pelosi, D-Calif., called the vote transformational, for the broad effects it would have on every household, business, industry and farm in the decades ahead. Republicans pointed mainly to higher energy bills for virtually everyone -- a lot higher for some.

Even with a 78-vote majority in the rule-bound House, Democratic leaders needed help from a few Republicans to pass the bill after 44 Democrats said no.

Pelosi's July agenda includes putting together a health care bill that could be considered in the fall.

In the Senate, Sen. Barbara Boxer, D-Calif., has the Senate Environment and Public Works Committee writing a global warming bill. It's using the House plan, which calls for a 17 percent reduction in greenhouse gases by 2020 and an 83 percent reduction by 2050, as a starting point.

But the Senate Finance Committee and the Senate Energy and Natural Resources Committee also will play big roles; a final product won't come together before fall.

Also on the July agenda are more House and Senate votes on the 12 annual spending bills for the budget year that begins Oct 1. The House has passed four of the 12; the Senate is scheduled to vote Monday on its first, covering what Congress spends on its own operations.

House leaders promise to try to pass all 12 bills by the end of July. Action in the Senate promises to be significantly slower.