When White House counsel Pat Cipollone argues President Donald Trump’s case in a Senate trial this week, he will also be defending his role in a controversial legal strategy that helped lead to Trump’s impeachment on a charge of obstructing Congress.

Democratic lawmakers in the House of Representatives said on Tuesday that evidence heard in their impeachment inquiry indicates he “played an instrumental role” in that obstruction and his representation of Trump threatens to undermine the integrity of the trial.

They have charged Trump with abuse of power for allegedly pressuring Ukraine to investigate a political rival, former Vice President Joe Biden, and obstruction of Congress for undertaking “an unprecedented campaign” to prevent them from probing those allegations.

In a letter sent to Cipollone just hours before the trial was set to begin in earnest, the lawmakers urged the White House counsel to disclose the full extent of his knowledge of Trump’s alleged pressure campaign and said evidence suggested his office had been directly involved “in potential efforts to conceal President Trump’s scheme from Congress and the public.”

There was no immediate comment from the White House.

One of the main pieces of evidence to support the obstruction charge against Trump is a widely criticized letter written by Cipollone on Oct. 8 in which he said Trump could not permit the administration to participate in the Ukraine investigation, which he described as an illegal attempt to remove a democratically elected president.

Cipollone’s letter thrust the lawyer to the forefront of the administration’s battle against the impeachment inquiry in the Democratic-led House of Representatives, bringing him public attention that friends and colleagues say he has long eschewed, unlike many of Trump’s lawyers.

The arguments and political tone in his letter, uncharacteristic for a White House counsel, drew rebukes from many legal experts, including former law school classmates, who said it distorted the law for “cable news consumption.”

While Cipollone declined to comment for this story, Jay Sekulow, another leading member of Trump’s legal team, defended him, saying the arguments in Cipollone’s letter were “exactly what the founders had in mind in crafting a constitution that respects separation of powers.”

Now Cipollone will be in a much brighter spotlight in a televised trial that will take him from his second-floor White House office - where he has a photograph of his family, including his 10 children, with Trump - to the Senate chamber, where he will help lead the Republican president’s defense.

The trial begins in earnest in the Senate on Tuesday.

Democrats have called for Trump’s removal from office, describing him as a danger to American democracy and national security. Trump and his lawyers say he has done nothing wrong and that Democrats are simply trying to stop him from being re-elected. Trump is expected to be acquitted in the trial in the Republican-controlled chamber.