Former Trump lawyer Michael Cohen is preparing to deliver scathing comments about President Donald Trump before Congress on Wednesday morning.

Meanwhile, Trump is in Vietnam with North Korea's Kim Jong Un. He is trying to secure a pledge to denuclearization and has been touting his warm relations with Kim.

Cohen is expected to accuse Trump of criminal conduct, racism, and lying.

His planned remarks include a quip about the "irony" that Trump is in Vietnam, despite having secured a dubious medical deferment from the Vietnam War.

His testimony will likely undermine whatever Trump brings back from Vietnam. Cohen's testimony was only finalized last week, after Trump's trip to Vietnam was booked.

Michael Cohen's explosive testimony to Congress is due Wednesday morning — and looks tailored to undermine whatever glory President Donald Trump hopes to achieve at his summit with North Korea's leader Kim Jong Un.

Cohen is testifying publicly before the House Oversight Committee at 10 a.m. ET on Wednesday, where he reportedly plans to detail Trump's alleged "illicit acts" and publicly accuse Trump of engaging in criminal conduct while in office.

He also testified before the Senate Intelligence Committee behind closed doors on Tuesday.

Meanwhile, some 8,300 miles away, Trump is meeting Kim in Hanoi, Vietnam, where he hopes to make more progress to secure the North Korean leader's pledge to abandon his pursuit of nuclear weapons.

Trump waves after a meeting at Vietnam's Presidential Palace in Hanoi on Wednesday. Luong Thai Linh/Pool via Reuters

According to a tentative deal which could be locked down at the summit — described to Vox by three people familiar with the talks — Trump and Kim could agree to formally end hostilities and improve ties between North and South Korea.

It also said North Korea could promise to stop producing materials for nuclear weapons, in exchange for some sanctions relief.

While this tentative deal falls short of complete and verifiable denuclearization — Trump's stated aim in North Korea — the president would likely take it as a win.

However, his ability to do that will likely be severely curtailed by the fallout from Cohen's testimony. And, according to leaked accounts of Cohen's planned remarks, Cohen has shaped his testimony specifically to needle the president during the summit.

A banner welcoming Trump and Kim at a South Korean restaurant in Hanoi. The two leaders are meeting on Wednesday and Thursday. Reuters/Kham

'I find it ironic, President Trump, that you are in Vietnam'

Cohen plans to deliver a quip about Trump's absence in Washington, DC, during his testimony and pair it with an unflattering statement about Trump's medical deferment from the Vietnam War, according to a leaked text of Wednesday's testimony published by CNN's Kevin Liptak.

Trump claimed to suffer from bone spurs, which ultimately prevented him from fighting in the Vietnam War.

Cohen is expected to say that Trump instructed him "not to answer the specific questions by reporters but rather offer simply the fact that he received a medical deferment."

Cohen is expected to add: "I find it ironic, President Trump, that you are in Vietnam right now."

Trump himself has felt compelled to address the impending testimony from Hanoi. On Wednesday, while preparing to meet Kim for dinner, he sent a tweet pre-emptively attacking the credibility of Cohen's testimony.

"Michael Cohen was one of many lawyers who represented me (unfortunately)," Trump tweeted. "He had other clients also. He was just disbarred by the State Supreme Court for lying & fraud."

"He did bad things unrelated to Trump. He is lying in order to reduce his prison time. Using Crooked's lawyer!" he added, likely referring to Cohen's lawyer Lanny Davis, who previously worked for Bill and Hillary Clinton.

He has appeared reluctant to discuss Cohen in front of Kim, though. When Associated Press reporter Jon Lemire asked Trump for his response to Cohen's testimony while sitting next to Kim, Trump simply shook his head, Lemire said.

The Cohen testimony deflates the optics of the Vietnam summit.

Trump had been touting the visit for weeks, making the announcement one of the centerpieces of his State of the Union address on February 5 where he claimed that his efforts to connect with Kim had prevented a war and saved millions of lives.

At the time, Cohen's planned testimony had been delayed indefinitely. It was not until February 20 that it was confirmed that Cohen's testimony would come while Trump was in Vietnam, by which time the details of the summit were already in place.

Cohen departs after testifying before the Senate Intelligence Committee behind closed doors on Capitol Hill on Tuesday. Associated Press

Democratic lawmakers on the House Oversight Committee plan to question Cohen extensively about hush-money payments made during the 2016 election to women who said they had affairs with Trump, according to an internal committee memo seen by Business Insider's Sonam Sheth.

The president denies the affairs and initially denied knowing anything about the payments.

Read more: Michael Cohen details hush-money payments in bombshell opening statement: 'Lying to the First Lady is one of my biggest regrets'

Details of Cohen's allegation of Trump's criminal conduct are also not clear, but The Wall Street Journal reported that they were related to a hush money payment that Cohen facilitated to Stormy Daniels, the porn star who says she had an affair with Trump.