Trump's Pentagon chief vows to cooperate with impeachment probe in apparent break with the president

US Defense Secretary Mark Esper said Sunday the Pentagon would cooperate with the congressional impeachment inquiry -- in an apparent break with President Donald Trump's policy to thwart the probe.

Esper said his department would try to comply with a subpoena from House Democrats seeking records relating to the withholding of US military aid to Ukraine.

"We will do everything we can to cooperate with the Congress," Esper said on CBS's "Face The Nation."

His reassurance came days after the White House announced it would not cooperate with the Democratic-led House of Representatives, calling its impeachment push illegitimate and unconstitutional.

Democrats are seeking information related to Trump pressing his Ukrainian counterpart to uncover dirt on 2020 US presidential contender Joe Biden -- and the alleged conditioning of military aid on that favor.

Democrats have slapped subpoenas on the Pentagon and White House, demanding documents tied to Trump's withholding of almost $400 million desperately needed by Kiev in its conflict with Russia over Moscow's 2014 annexation of Crimea.

Esper told "Fox News Sunday" that administration officials and Trump himself may place restrictions on the release of documents demanded by the subpoena.

"I don't know the status of what that document preparation is. I don't know what restrictions they will have internally," Esper said.

"The White House has a say on the release of documents as well. There are a number of things that play into this."

Democrats obtained a string of text messages between US diplomats that showed the Trump administration's effort to pressure Ukraine into investigating Biden and his son Hunter, and that some diplomats in the text chain expressed concern that such actions were inappropriate.

- 'Absolutely illegal' -

On Tuesday, Trump's White House counsel Pat Cipollone sent senior Democrats an eight-page letter declaring the inquiry illegitimate. The letter has been rejected by experts as having little legal basis.

The Democrats' subpoenas focus in part is on Trump's July 25 call with Ukrainian President Volodymyr Zelensky.

A released rough transcript of the call shows the two leaders discussed Zelensky's desire to receive the military aid, followed by Trump responding that "I would like you to do us a favor though," and then bringing up Biden.

Esper was asked by Fox News if Trump had explained why he held up the aid, against the guidance of the Pentagon, and replied: "I have nothing to share with you on this."

Details of the call emerged last month in an explosive whistleblower complaint by an unidentified intelligence official.

The scandal is unusual in that the conduct in question -- Trump soliciting an investigation of a potential 2020 election rival from a foreign country -- is acknowledged by both sides.

At dispute is whether the phone call constituted a crime or an impeachable offense.

Federal Election Chairwoman Ellen Weintraub has declined to discuss the specifics of Trump's case.

But she told MSNBC earlier this month that "the law is pretty clear... It is absolutely illegal for anyone to solicit, accept, or receive anything of value from a foreign national in connection with any election in the United States."

Sunday's morning talk shows, in a repeat of last week, were notable for the absence of key administration officials willing to publicly defend Trump's actions.

Former Ohio governor John Kasich told CNN's "State of the Union" that his fellow Republicans needed to "look in the mirror" and speak out on the Ukraine call.

"Figure out how you want to be remembered later... There's nothing wrong with telling the truth and sharing your real feelings," he said.

"I think at the end of the day, the evidence is there to impeach Trump," Senator Bernie Sanders, a 2020 Democratic presidential hopeful, told ABC's "This Week."

But he added that the "real issue" is whether top Senate Republican Mitch McConnell will "do the right thing" if Trump is impeached, setting the stage for a trial in the US legislature's upper house.

"I am nervous that McConnell will put party in front of country," Sanders said.