Democrats are using old clips of President Donald Trump's remarks to undermine his defense during the Senate impeachment trial.

Republicans have so far prevented new witnesses from appearing in the trial — but Democratic impeachment managers on Thursday played a clip from December in which Trump himself said he wanted to hear testimony from top White House officials.

In another clip played during the trial, from October, Trump said of Ukraine: "They should investigate the Bidens."

Clips of Trump's prominent defenders were also played at the trial, including one in which Sen. Lindsey Graham could be seen in 1999 flatly contradicting his current position on impeachment.

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Republicans have stuck to a central argument in their defense of President Donald Trump in the impeachment trial: that in seeking an investigation of the Ukrainian energy firm Burisma — where former Vice President Joe Biden's son Hunter worked — Trump was simply acting out of concern to address corruption in Ukraine.

There's just one person whose words and actions keep blowing up that defense: the president himself.

During impeachment proceedings this week, Trump's voice rang through the Senate chamber as Democrats played multiple clips meant to portray Trump as unconcerned with tackling corruption in Ukraine but rather with securing information to damage Biden, a 2020 Democratic presidential contender.

'From the president's own words ...'

A clip from last October showed Trump doubling down on his call for Ukraine to announce an investigation into Biden and calling too on China to get involved and launch its own Biden investigation.

"Well, I would think that if they were honest about it, they'd start a major investigation into the Bidens," Trump said of Ukraine. "It's a very simple answer."

"So here we hear again from the president's own words what his primary object is," Rep. Adam Schiff, the lead House impeachment manager at the Senate trial, told the upper chamber Thursday.

"And his primary object is helping his reelection campaign, help to cheat in his reelection campaign."

Schiff also used a clip of the president from December in his argument against the Republican decision thus far to prevent new witnesses from testifying. In the clip, he mentioned Secretary of State Mike Pompeo; his acting chief of staff, Mick Mulvaney; and then-Energy Secretary Rick Perry.

"I would love to have Mike Pompeo and Mick, and I would love to have Rick Perry, and many other people testify," the president said at the time.

It is worth noting, however, that in the full clip — which wasn't played — Trump went on to say: "I don't want them to testify when this is a total fix," referring to impeachment proceedings.

Top Trump defenders aren't safe from scrutiny either

The president isn't the only one whose words are being turned against him — his top impeachment allies are, too.

Trump's legal team and some Republican lawmakers, including Sen. Lindsey Graham, are arguing that that only a crime can be grounds for impeaching presidents and removing them from office.

Abuse of power and obstruction of Congress, the charges used to impeach Trump, are simply not crimes so can't be used to impeach, he has said.

But in footage played by Democrats on Thursday, from President Bill Clinton's impeachment trial in 1999, Graham could be seen arguing a different position.

"I think that's what they meant by high crimes," Graham said. "Doesn't even have to be a crime. It's just when you start using your office and you're acting in a way that hurts people, you've committed a high crime."

Trump's no-holds-barred, unfiltered style is at the heart of his appeal to his supporters, and it's not the first time his words have been returned to haunt him.

During legal battles over Trump's hardline anti-migration policies last year, lawyers successfully argued that his long record of racist remarks could be used in court to undermine his arguments.