"Any reporting to the contrary, and any testimony provided to Congress, is simply false, and any current or former staff who suggest I have raised or discussed Ukraine matters with President Trump, are similarly misinformed or spreading outright falsehoods."

Why it matters: Trump's former top Russia adviser, Fiona Hill, told impeachment investigators that she heard Trump thought Patel was his Ukraine director and that Patel was slipping Ukraine-related "materials" to the president outside of the normal NSC channels. Patel has never been assigned to Ukraine on the NSC.

Democrats on the House Intelligence Committee seized on Hill's allegations about Patel, who previously worked for ranking member Devin Nunes (R-Calif.) and who helped write a memo that accused the Russia investigators of bias.

Between the lines: Hill said that when she heard from another NSC staffer about Patel's supposed involvement on Ukraine, she considered it to be so "strange" and alarming that she reported it to her superior.

Hill said, however, that she never found out what actually went on with Patel and that her superior, Charles Kupperman, never got back to her after telling her he'd look into the matter.

Lt. Col. Alexander Vindman, an NSC official who testified before impeachment investigators, also mentioned Patel in his testimony.

Vindman testified that Hill told him that Patel was misrepresenting himself as an Ukraine expert and the president had come to believe Patel was in charge of Ukraine policy on the NSC.

In a statement Friday night, Patel categorically denied all of these allegations from his current and former colleagues.

"I pride myself on my record as a dedicated national security professional who is entrusted to handle our nation's most sensitive matters," he said. "At no time have I strayed from my mission to protect the homeland in service to President Trump and the National Security Council."

Go deeper: Vindman says Mulvaney coordinated plan to push Ukraine for Biden investigations