Vice President Mike Pence will remain in Washington next week to preside over the Senate’s vote on the Republican tax overhaul bill, his chief spokeswoman said, a signal GOP leaders expect to thread the needle.

“Yesterday the White House informed Senate Leadership that due to the historic nature of the vote in the Senate on tax cuts for millions of Americans, the VP would stay to preside over the vote,” Alyssa Farah, Pence’s press secretary, said in a statement. “The Vice President will then travel to Egypt [and] Israel where he’ll reaffirm the United States’ commitment to its allies in the Middle East and to working cooperatively to defeat radicalism.

“He looks forward to having constructive conversations with both [Israeli] Prime Minister [Benjamin] Netanyahu and [Egyptian] President [Abdel-Fattah] el-Sisi to reaffirm President Trump’s commitment to our partners in the region and to its future,” she said.

Watch: Schumer Calls on McConnell to Delay Tax Vote Until Jones Is Seated

The questionable attendance of Sens. John McCain of Arizona and Thad Cochran of Mississippi, who both face health complications, raises doubts about whether the GOP will have the requisite votes.

Further complicating matters, at least two GOP senators are not sure bets. Florida Sen. Marco Rubio signaled Wednesday he is not yet ready to support the emerging GOP measure being crafted by a House-Senate conference committee. Tennessee Sen. Bob Corker previously voted against the Senate’s version over concerns it would balloon the federal deficit.

If both oppose the conference panel’s compromise bill, Pence’s vote would be needed as the 51st and decisive one.