(CNN)The Senate deadlocked 49-49 for about an hour Wednesday on a vote to break a filibuster of Rep. James Bridenstine, R-Oklahoma, to be the next NASA administrator until Sen. Jeff Flake, R-Arizona, returned to the floor and switched his vote to yes.
The motion then passed on a partisan 50-48 vote. Flake, a vocal critic of the President's, had been the only Republican to vote against Bridenstine.
Typically, when a vote like this is tied, Vice President Mike Pence would come to the chamber and break it. But he was in Mar-a-Lago with the president making that an impractical alternative.
Both Sen. John McCain, an Arizona Republican, who is ill, and Illinois Democratic Sen. Tammy Duckworth, who just had a baby, were absent.
The party-line vote against Bridenstine reflects the steep opposition from Democrats about President Donald Trump's nominee to head the space agency, who they believe is not a "space professional" in the words of Sen. Bill Nelson, a Florida Democrat. One Republican, Sen. Marco Rubio of Florida, had previously expressed concerns about Bridenstine but voted for him in the end.
Democrats also complained about his views on climate change.
"NASA is one of the few remaining areas that has largely avoided the bitter partisanship that has invaded far too many areas of government and our society today," Nelson said in a floor speech.
When he was nominated, Sen. Ted Cruz, R-Texas, called Bridenstine a "strong, principled and effective leader" who will "work hard to advance our national space policy goals, expand human space exploration and secure America's leadership in space."
A final confirmation vote for Bridenstine is expected Thursday.