The Senate approved a Republican budget resolution just after 3:00 a.m. Friday morning in a 52-46 vote, capping a grueling day of floor work that required lawmakers to take sides on dozens of amendments.

Republicans could only afford three defections on the budget, since no members of the Democratic caucus supported it. That left GOP leaders with little margin for error as they sought to approve the plan, which calls for cutting $5.1 trillion from federal spending over 10 years.

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Still, the fight is far from over.

The House passed its own budget resolution Wednesday, which means that the two chambers will now have to form a conference committee to resolve their differences after the Easter recess.

Earlier Thursday, McConnell said the Republican budget delivers on the promises the party made in 2014, when voters returned them to power in the upper chamber for the first time in eight years.

“They called for change, and today, the Senate is delivering that change,” McConnell said.

The White House dismissed the Senate GOP budget in a statement released Friday morning. It said the budget relied on gimmicks and placed the burden of deficit-reuction on the middle class, seniors and children.

While passage of the Senate budget was expected, the votes of Cruz, Rubio and Paul remained a mystery for most of the day.

Cruz, the only Republican to formally declare his presidential candidacy, said he was still undecided before the “vote-a-rama” began.

“I’m still assessing it. I’m looking at it carefully and I’ll make a decision by the time the vote comes up,” Cruz said.

The spotlight was on the 2016 contenders throughout the "vote-a-rama," which gave all of them a chance to bring forward policy proposals that they could tout on the campaign trail later this year.

Paul, who faces skepticism in the GOP for his views on foreign policy, proposed an amendment to raise defense spending by nearly $190 billion over the next two years. The Senate refused to advance it, voting 4-96, with Cruz and Rubio both opposing it.

Graham, another Republican eyeing a run for the White House, voted for the budget plan. He was responsible for a provision that would increase war funding for the Pentagon to $96 billion.

A deal to end the marathon session was reached after the Senate recessed shortly after 1 a.m., and Republicans huddled to discuss a way forward. The Senate came back into session about an hour later, after Democrats and Republicans culled hundreds of submitted amendments down to three more for each side.

During the long “ vote-a-rama ,” senators from both sides of the aisle offered amendments that were intended to make members of the opposing party squirm, with some votes likely to become fodder for campaign ads next year.

Many of the amendments proposed the creation of deficit-neutral reserve funds for certain issues, which would essentially serve as placeholders for later negotiations.

Democrats won approval on an amendment requiring up to seven paid sick days for workers, an issue that they believe could be potent in the 2016 campaign. Cruz, Rubio, Paul and Graham all voted against it.

Republicans, meanwhile, won passage of an amendment to increase awareness of any ObamaCare tax included in monthly insurance premiums, and another that would block a federal tax on carbon emissions.

The Senate also unanimously adopted an amendment that backs imposing additional sanctions against Iran if the U.S. president cannot confirm that the Iranian government is complying with any future nuclear deal.

Another amendment attached to the budget calls for repealing the federal estate tax.

Passing budgets in both chambers is only the first hurdle for Republicans, who want to use the budgetary process to take on President Obama.

Their next challenge will be reaching a joint conference agreement on the budget, which Republicans haven’t done since 2005.

Republicans are determined to get a budget through, since it will not require a signature from Obama and could lay the groundwork for repealing the healthcare law in a deficit-reduction package later this year.

“I’ve always thought that fundamentally their ideas are good and supported them. I think that’ll be the mood of most people here.”

If a joint conference agreement does pass both chambers, Republicans will be able to trigger a budget procedure known as reconciliation that could be used to target ObamaCare, reform the tax code and raise the debt ceiling, among other things.

Bills written under reconciliation rules cannot be filibustered in the Senate, freeing McConnell from the need to find Democratic votes.

While the two GOP budgets are similar, important differences could make it difficult to reconcile them. Enzi’s blueprint would balance in 10 years by cutting $5.1 trillion. The House budget, prepared by his counterpart Rep. Tom Price (R-Ga.), would balance in nine years by cutting $5.5 trillion.

Enzi’s plan doesn’t reform Medicare, but honors Obama’s request to find $430 billion in savings for the program. Price’s plan would partially privatize Medicare by converting it to a premium support system.

Both budgets would transform Medicaid into block grants. Neither plan offers a major overhaul to Social Security.

Despite the differences, parts of their two documents closely resemble each other in major ways, particularly on the push to repeal ObamaCare.

Both the House and Senate GOP budgets keep in place the spending limits known as sequestration that were imposed under a 2011 budget law. The Defense Department’s base budget in both blueprints is $523 billion, while the ceiling for non-defense domestic programs is $493 billion.

Just like the Senate, the House budget would approve $96 billion for the war fund next year — money that wouldn’t be subject to sequestration cuts.

There’s a caveat to the plan, however. In Enzi’s budget, a 60-vote point of order would be imposed against any spending bill that would increase the war fund above $58 billion. That means it would need a supermajority of 60 votes to win approval.

Altogether, the Senate budget would cut $4.3 trillion in mandatory spending over the next 10 years and $97 billion from discretionary programs.