Things got heated on Capitol Hill Tuesday during the second day of confirmation hearings for Neil Gorsuch, Donald Trump’s nominee for the U.S. Supreme Court seat that has been vacant since Justice Antonin Scalia’s death in February 2016.

Senator Sheldon Whitehouse, a Democrat from Rhode Island, wanted to know why a dark money organization had spent millions to stop President Obama’s nominee, Merrick Garland, from even getting a hearing last year, and has continued to spend millions supporting Gorsuch’s nomination.

“What’s interesting is that this group sees a huge difference between you that I don’t understand,” Whitehouse said pointedly to Gorsuch after Gorsuch refused to describe the differences in judicial philosophy between himself and Garland.

“The dark money group that is spending money on your election spent at least $7 million against him getting a hearing and a confirmation here, and indeed produced that result by spending that money,” Whitehouse said. And then, now, we have $10 million going the other way. That’s a $17 million delta and for the life of me I’m trying to figure out what they see in you that makes that $17 million delta worth their spending. Do you have any answer to that?”

“You’d have to ask them,” Gorsuch responded.

“I can’t, because I don’t know who they are,” Whitehouse said. “It’s just a front group.”

Whitehouse then challenged Gorsuch to disavow dark money, which is money spent for political purposes without any public record of the names of donors.

“You could ask right now as a matter of courtesy, as a matter of respect for the process that anybody funding this should declare themselves right now so we can evaluate who is behind this effort,” Whitehouse said.

Gorsuch declined, saying it was a “politics question” and that he would not get into politics. If Whitehouse didn’t like it, he said, “pass disclosure laws.”