John McCain, Hillary Clinton and Barack Obama stepped into unfamiliar territory Thursday: the U.S. Senate.

The three presidential candidates took a brief respite from the presidential campaign and returned to Washington to vote on a budget resolution that carries an amendment calling for a one-year moratorium on earmarks.

None of the candidates has been back for votes since February, according to the Senate Radio and Television Gallery. McCain voted on Feb 13 on an Indian health care bill. Obama voted last on Feb. 12 on a procedural vote to end debate on the terrorist surveillance program and Clinton last was in the Senate for a vote on Feb. 6 for a cloture vote on an economic stimulus package. The gallery was still researching the last time all three were in the Senate at the same time for votes, which dates back to at least last year.

As usual the day's events were being watched closely for signs of mis-staging or errant unscripted moments among the White House wannabes. While McCain was on Capitol Hill early, avoiding any morning missteps, Clinton and Obama arrived nearly simultaneously, forcing Clinton to wait out her entrance as Obama, exited his car, drawing media cameras to him just as Clinton's motorcade arrived.

Later on the floor, McCain and Clinton spoke briefly and McCain and Obama were captured out of earshot in deep discussion. McCain approached Obama and Obama motioned for the two to step aside. McCain spoke first and then Obama responded and appeared to do most of the talking. The exchange lasted about two minutes.

Photographers blanketed the Capitol for the candidates throughout the day. Obama was spotted cooling his heels just off the Senate floor in the office of his lead supporter, Senate Majority Whip Dick Durbin . One photographer shouted gleefully to another, "I got him!"

Another interesting meeting also went on for 10 minutes among Obama, Florida Sen. Bill Nelson and Michigan Sen. Debbie Stabenow. All three appeared to be talking passionately, gesturing to each other. Florida and Michigan have been trying to work through a compromise on getting their delegates counted at the Democratic national convention in August, but a resolution has been elusive.

Thursday's vote-a-rama is a tradition that dates back to the 1974 Budget Act, which requires 50 hours of debate on the budget resolution, the annual blueprint for all 12 spending bills, and mandates that an unlimited vote-fest occur at the very end.

Earmarks are one issue in which Republicans think they have a leg up on Democrats in Congress. In its vote-a-rama, the Senate is expected to vote on the amendment sponsored by South Carolina Republican Sen. Jim DeMint calling for a one-year moratorium on earmarks, though some senior members were trying to delay and possibly block the vote.

As for McCain, he slammed Obama and Clinton for being late to the game when it comes to ending earmarks, a signature issue for the Arizona senator. He said it would behoove both candidates to disclose earmarks -- or home state spending projects that skirt the normal legislative channels -- they have requested and won.

Though Clinton has declined to release any of her annual earmark requests, Obama answered the taunt Thursday, releasing his earmark requests for 2005 and 2006, his first two years in the Senate. The requests are available on his campaign Web site.

Obama pivoted to goad Clinton into doing the same. Spokesman Robert Gibbs said in a statement if she doesn't disclose her earmarks, "voters should ask why she doesn't believe they have the right to know (how) she wants to spend their tax dollars."

But McCain still wagged his finger at both of them for requesting the earmarks in the first place.

In both Clinton and Obama's cases, they have requested "hundreds of millions of dollars of taxpayers dollars that are absolutely, outrageously wasted," McCain said. "I think they should ask that those earmarks that they asked for and obtained-- the money hasn't been spent yet -- ask them to turn that money back to the treasury."

Ahead of the meetings, the candidates offered their commentary on their opponents' records in the Senate. Democrat Obama accused Republican McCain of reversing his position on President Bush's 2001 and 2003 tax cuts to win over Republican voters.

McCain voted in an early tally for the cut to be included in the resolution. Clinton and Obama voted against them. The amendment failed on a partisan 52-47 vote.

"He made a decision to reverse himself on that," Obama told reporters as he flew from Chicago to Washington. He noted McCain had originally voted against the cuts, which McCain said he did because the bills didn't offer commensurate spending cuts.

"That was how, I guess, you got your ticket punched to be the Republican nominee," Obama said of McCain. "But he was right then, and he's wrong now."

McCain has said he now supports extending the tax cuts, which are set to expire in 2011, because the economy is struggling and tax reductions offer some stimulus.

Obama has proposed an array of subsidies for higher education, health care and other costs hitting middle-class families. He said he believes he can pay for such plans by closing tax loopholes, placing a new tax on carbon emissions, phasing out the Iraq war and ending the Bush tax cuts for the nation's highest earners.

"We have identified the cuts that we think are available, or the changes in our tax code that are available to pay for our middle-class tax cut as well as our proposals to fund higher education and so on," the Illinois senator said.

He added, however, "There will be a lot of special interests and lobbyists that will resist the kinds of changes that I've proposed."

Asked if he would scale back his agenda if some of his proposed tax increases fail, Obama said, "I am a strong believer in pay-go," a term for avoiding new deficits by paying as you go. "So adhering to pay-go means that if I couldn't find the revenues or reduce spending in other areas, then I couldn't pay for my proposals."

The Club for Growth, a spending watchdog that supports traditional conservative economic principles on Thursday urged Clinton to join a moratorium that Obama and McCain have both pledged to take.

"As presidential candidates, Senators McCain, Obama, and Clinton are promoting themselves as leaders of the country," said Club for Growth President Pat Toomey. "But being a leader means doing the right thing even when everyone else isn't. "John McCain has long been a leader on the issue of wasteful spending, and Senator Obama has now recognized the importance of leading by example. What is Hillary Clinton waiting for?"

FOX News' Trish Turner and Mosheh Oinounou and The Associated Press contributed to this report.