Story highlights Sen. Bill Nelson derided Bridenstine for his past political rhetoric.

Bridenstine also came under fire for his past views on climate change and lack of background in science.

(CNN) President Donald Trump's pick for the top job at NASA, Rep. James Bridenstine, faced blistering critique at his Senate confirmation hearing Wednesday, with Democrats questioning his fitness for the role.

Sen. Bill Nelson, the ranking member on the Senate Committee on Commerce, Science & Transportation and a former astronaut, derided Bridenstine for his past political rhetoric and opinions on climate change. The Florida Democrat suggested that these comments precluded Bridenstine from the position.

"As I have said, NASA is a family. This committee has heard me say many times NASA is not political. The leader of NASA should not be political. The leader of NASA should not be bipartisan; the leader of NASA should be nonpartisan. And when that has occurred when it has been partisan in the past, we've had a disaster," Nelson said in his opening remarks.

"Your recent public service career does not instill the confidence about your leadership skills or ability to bring people together. Unity is so important in NASA instead of division. What your record is ... your record and your behavior in Congress has been as divisive and extreme as any in Washington," he continued, citing to the Oklahoma Republican's criticisms of former President Barack Obama and Sen. Marco Rubio, his endorsement of Kelli Ward over Sen. John McCain in Arizona and his anti-LGBT platform, such as his 2013 opposition to same-sex marriage

"NASA represents the best of what we can do as a people. NASA is one of the last refuges from partisan politics. NASA needs a leader who will unite us, not divide us. Respectfully, Congressman Bridenstine, I think you've got a long way to go to prove to be that leader," Nelson concluded.

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