Senate Republicans are pushing forward with a budget that is key to accomplishing their goal of passing tax reform this year.

Senators voted 50-47 to start debate on the fiscal year 2018 budget, which includes instructions allowing Republicans to avoid a Democratic filibuster when they pass their tax plan.

With a 52-seat majority, Republicans can only afford to lose two senators, if every member of the Democratic caucus votes no, to pass the budget with Vice President Pence breaking a 50-50 tie.

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Sen. Rand Paul Randal (Rand) Howard PaulSecond GOP senator to quarantine after exposure to coronavirus GOP senator to quarantine after coronavirus exposure The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill MORE (R-Ky.) voted to start the debate Tuesday after blasting a pair of the Senate's defense hawks over the budget.

"Senators [John] McCain and [Lindsey] Graham are torpedoing the budget by insisting on busting the budget caps for more spending,” Paul said in a tweet.

Paul is remaining tight-lipped on whether he will ultimately vote against the budget during a final vote later this week, but he's viewed as the caucus's most likely no vote.

Leadership will need to balance demands from Paul, who told reporters he is in talks with the White House, with absences that leave them with no room for error.

Sen. Thad Cochran William (Thad) Thad CochranEspy wins Mississippi Senate Democratic primary Bottom Line Mike Espy announces Mississippi Senate bid MORE (R-Miss.) is recovering from health issues, and Sen. Richard Shelby Richard Craig ShelbySenate GOP eyes early exit Dems discussing government funding bill into February GOP short of votes on Trump's controversial Fed pick MORE (R-Ala.) is out of Washington for a funeral on Tuesday.

Sen. John Kennedy John Neely KennedyMORE (R-La.) predicted that his caucus will be able to get enough support to pass the budget because most lawmakers view it as a necessary stepping stone to being able to pass tax reform.

“I think people understand that it’s more about tax reform than the budget, and it’s a necessary step so we can move to tax reform," he said.

Republicans got a little more breathing room with Sen. Bob Menendez Robert (Bob) MenendezKasie Hunt to host lead-in show for MSNBC's 'Morning Joe' Senators ask for removal of tariffs on EU food, wine, spirits: report VOA visa decision could hobble Venezuela coverage MORE (D-N.J.) — who is in the middle of a bribery and corruption trial — missing Tuesday's vote. His office has not said if he will be in Washington for a final vote on the budget.

Tuesday's vote kicks off roughly two days of debate on the Senate floor and a marathon session — known as a vote-a-rama — before senators can take a final vote on the budget.

The vote-a-rama is expected to start on Thursday and run late into the night, meaning a final vote on the budget is likely to take place on Thursday night or early Friday morning.

The Senate's budget would cut nondefense spending starting in 2019 and result in up to $106 billion by 2027. It would also only cut mandatory spending by $1 billion, compared to the House version’s $203 billion.

It would also allow the Senate GOP's tax plan to add up to $1.5 trillion to the deficit over a decade.

Niv Elis contributed