Sen. Rand Paul (R-Ky.) called for an investigation into four Democratic senators over a letter that they sent to Ukraine in 2018 that threatened to withhold aid from the country if it did not cooperate in investigating President Trump.

When asked by NBC “Meet the Press” host Chuck Todd on Sunday, Oct 13, whether he was concerned over the president’s personal attorney Rudy Giuliani’s interaction with Ukraine, Paul pointed out that Democrats were first to enlist Ukraine in U.S. elections.

“I think what’s interesting about this is both sides seem to be doing the same thing. If anything is consistent here, it’s that both parties have tried to involve themselves in Ukraine,” Paul said.

“So for example, four senators, Democrats, wrote a letter to the Ukrainian government and said, ‘If you don’t keep investigating Trump we may reconsider our bipartisan support for your aid.” Both parties seem to be doing this,” he added.

Paul asserted the letter was a threat and that needs to be examined.

“Someone needs to actually, in an objective way, evaluate a letter from four Democrats (…) That’s a threat,” Paul said. “And that’s the same kind of stuff they’re accusing Trump of. But nobody’s talking about that the Democrats are doing exactly the same thing.”

The 2018 letter Paul referred to was sent by three Democratic senators—Sens. Robert Menendez (N.J.), Dick Durbin (Ill.) and Patrick Leahy (Vt.)—to Ukraine’s prosecutor general, Yuriy Lutsenko. In the letter, they expressed their “great concern” over reports that Ukrainian officials might not cooperate with the Mueller investigation.

The fourth Democratic senator was Chris Murphy (D-Conn.). According to the Hill‘s John Solomon who wrote that Murphy told Ukrainian President Volodymyr Zelensky that the U.S. aid dedicated to the country “could be jeopardized if the new president acquiesced to requests by President Trump’s lawyer Rudy Giuliani to investigate past corruption allegations involving Americans, including former Vice President Joe Biden’s family.”

Speaking on former Vice President Joe Biden and his son’s Ukraine scandal, Paul said that Hunter Biden earned $50,000 per month working on a board of a Ukrainian natural gas company while his father was vice president “doesn’t pass the smell test.”

“I think most people do think there was some corruption involved with Hunter Biden. And I hope we do get to the bottom of it,” he said.

On “Fox & Friends” on Monday, Paul doubled down on his call for a probe into these senators, saying, “Democrats get to threaten Ukrainian aid and nothing happens to them. Now they want to impeach a president over this? If you’re going to condemn Trump, you need to condemn the Democratic senators.”