President Trump blasted House Democrats for ramping up calls to impeach him after reports said he withheld military aid to coerce Ukraine to launch an investigation into his political rival Joe Biden.

“I think it’s ridiculous. It’s a witch hunt. I’m leading in the polls. They have no idea how they stop me,” Trump said Tuesday as he arrived at the United Nations. “The only way they can try is through impeachment. This has never happened to a president before.”

Several reports on Tuesday said that Trump ordered his administration to hold up nearly $400 million in aid to Ukraine a week before his phone call with the country’s president in which he pushed for an investigation into Biden’s son Hunter.

Trump said the funds were “fully paid” and pressed Europe to pay their share to Ukraine.

“Just the United States. We’re putting up the bulk of the money. And I’m asking why is that?” ​Trump questioned at the UN, where he was scheduled to address the General Assembly. “Why is it only the United States putting up the money? And by the way, we paid that money.​”

House Speaker Nancy Pelosi is expected to meet with Democratic leaders Tuesday afternoon ​​to discuss Ukraine.