A confluence of events put President Donald Trump’s nominee to lead NASA on the verge of an unexpected blockade Wednesday afternoon.

Republican Sen. Jeff Flake of Arizona had initially voted against limiting debate on the nomination of GOP Rep. Jim Bridenstine of Oklahoma, but after almost an hour, he switched his vote.

While Flake was recorded against the cloture motion on Bridenstine, the vote was deadlocked 49-49. His reversal allowed the nomination to move forward 50-48. A confirmation vote is likely before the Senate wraps up work for the week on Thursday.

Under the normal course of events, a generally partisan tie vote could have been overcome with the assistance of Vice President Mike Pence, voting to break the tie in favor of Trump’s nominee.

Wednesday, however, Pence was joining Trump for meetings with Japanese Prime Minister Shinzo Abe at the president’s Mar-a-Lago resort in South Florida. So the Senate would have needed to hold open the Bridenstine vote, potentially for hours.

All 98 of the 100 senators expected to be available to vote Wednesday were present, with John McCain battling brain cancer in Arizona and Tammy Duckworth, an Illinois Democrat, taking leave after giving birth on April 9.

The Senate is considering a Duckworth resolution to allow children under the age of 1 on the chamber floor, and the Bridenstine vote situation underscores the significance of the resolution. Had Duckworth been present she might have been able to defeat cloture on the nomination.

Bridenstine, who had previously announced he would not run for re-election when his current third term in the House expires, was a naval pilot who flew combat missions in Iraq and Afghanistan.

Among his legislative accomplishments are provisions of a law that authorized the operations of NASA and sought to promote space science and a manned mission to Mars, but he has faced persistent questions about his qualifications to lead the space agency.

Pence will be “in DC and able to break a tie, if needed,” a Pence aide said via email when asked about the nomination of Bridenstine to be NASA chief, adding that the vice president is confident the House member from Oklahoma will win the support to be confirmed.

When the Senate Commerce, Science and Transportation Committee considered the Bridenstine nomination in January, ranking Democrat Bill Nelson of Florida predicted the nomination could be doomed on the floor.

“Congressman Bridenstine has no experience managing a large organization or program, no background in science or engineering, and a history of political divisiveness,” said Nelson, who famously traveled aboard the space shuttle Columbia as a payload specialist while serving in the House.

Ed Pesce and John T. Bennett contributed to this report.