House Budget Committee Chairman John Yarmuth on Friday jumped into the impeachment controversy surrounding President Donald Trump, demanding that the White House hand over documents related to why foreign aid for Ukraine was delayed.

Trump never made an explicit reference to the roughly $400 million aid package during his July call with Ukrainian President Volodymyr Zelensky.

But the money had been put on hold days before the controversial phone call in which Trump urged the foreign leader to open a corruption investigation into former Vice President Joe Biden, a Democrat running for president.

Yarmuth, a Democrat from Louisville, wrote a Friday letter along with House Appropriations Committee Chairwoman Nita Lowey seeking answers from the Trump administration about the delayed aid.

In the letter to acting White House Chief of Staff Mick Mulvaney, the lawmakers say they "have serious concerns that recent apportionment actions by the Office of Management and Budget to withhold military aid for Ukraine and other foreign assistance."

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Yarmuth and Lowey argue such a move by the Trump administration violates the Impoundment Control Act of 1974, which specifies the president may request Congress rescind appropriated funds.

The lawmakers say Trump delaying the funds unilaterally is "an abuse of the authority provided to the president to apportion appropriations." They are asking Mulvaney for a number of documents and specific questions that look to establish a timeline explaining when, why and how Trump withheld Ukraine's aid.

"Congress maintains the power of the purse and is obligated to address executive branch overreach," budget committee spokeswoman Alexandra Weinroth said in a news release. "Chairs Lowey and Yarmuth are committed to protecting and meeting those responsibilities."

Senate Majority Leader Mitch McConnell, a key Trump ally, told reporters in Washington this week he never received an explanation from the Trump administration about why Ukraine's aid was withheld.

"I’m grateful that security assistance has been released to help our friends in Ukraine defend themselves," McConnell said.

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McConnell said he had been pressing Trump's Cabinet secretaries and other officials about the aid package to ensure the U.S. did not back away from those commitments.

The GOP leader said this week how it is important for him the U.S. stand with Ukraine, especially as a firewall against Russian President Vladimir Putin's aggressive actions in the region.

"The best way to contest Putin and his hegemonic aspirations is to rebuild our defenses, work closely with our allies and partners and improve the capacity of those threatened by Moscow to defend themselves," McConnell said.

The senator's office did not immediately respond to a request for comment about whether he supported Yarmuth's letter requesting additional documents surrounding the aid package.

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Reach Phillip M. Bailey at pbailey@courier-journal.com or 502-582-4475. Follow him on Twitter at @phillipmbailey.