Testimony by Michael Cohen, Trump's former personal lawyer, could eclipse US-North Korea summit Donald Trump and Kim Jong Un meet while Michael Cohen testifies on Capitol Hill.

Congressional testimony by President Donald Trump's former personal lawyer Michael Cohen on Wednesday threatens to cast a shadow over the president's second summit with North Korean leader Kim Jong Un, as Republicans argue the timing amounts to Democrats attempting to "distract" from the president's diplomatic efforts.

Eight months after the summit in Singapore between Trump and Kim ended in a vague declaration about the "denuclearization of the Korean Peninsula," his administration hopes to put make further progress on that front this week as the two meet in Vietnam.

The summit's stakes for Trump are also personal.

During a freewheeling national emergency declaration-related press conference on Friday, President Donald Trump also claimed that Japanese Prime Minister Shinzo Abe nominated him for the Nobel Peace Prize for those efforts after his first meeting with Kim. Japanese newspaper Asahi Shimbun reported Abe wrote a letter of recommendation for Trump to receive the prize, but it was after the U.S. government "informally" made the request.

The Trump administration is pushing for concrete steps toward its goal of dismantling North Korea's nuclear weapons program. But the U.S. intelligence community and several top experts have warned that North Korea has no interest in giving up its nuclear weapons, which it sees as critical the Kim regime's survival, instead playing for time and sanctions relief.

Meanwhile, as the high stakes summit between the two leaders prepared to get underway, Cohen appeared behind closed doors before the Senate Intelligence Committee in Washington on Tuesday for his first of three congressional hearings this week, and will testify publicly before the House Oversight Committee Wednesday.

A source familiar with Cohen's testimony said he's expected to accuse Trump of potentially committing a crime while in office, a claim which could come mere hours before Trump and Kim come face-to-face in Vietnam.

“I really appreciate the opportunity given to me to clear the record," Cohen told reporters after his appearance before the Senate Intelligence Committee behind closed doors Tuesday. "I look forward to tomorrow to - in my voice - tell the American people my story and I’m going to let the American people decide exactly who’s telling the truth.”

Cohen's appearance was first announced in January but postponed three times due to reasons ranging from his expressing fears for his personal safety to "post-surgery medical needs."

And while there's no evidence that the rescheduled dates were intended to coincide with the president's travel overseas, Republicans accused Democrats of openly trying to scuttle Trump's efforts to convince North Korea to give up its nuclear ambitions.

"It’s sad Democrats are wasting time with this liar in an effort to distract from the historic progress [Trump] is making overseas," Republican National Committee chairwoman Ronna McDaniel said in a tweet Tuesday.

Though Cohen previously served as the Republican National Committee's deputy finance chair up until June of last year, the committee continued its pile-on with a video montage of Cohen lavishing Trump with praise on cable TV shows during his run for the White House.

At the end of the video compilation, text appears: "HAVE FUN IN PRISON!"

Cohen is scheduled to report to prison in early May for a three-year sentence after pleading guilty in November to lying to Congress.

In a separate statement Tuesday, White House press secretary Sarah Sanders continued to call Cohen a liar and hit Democrats for giving him a platform to attack the president.

The president's son, Donald Trump Jr., similarly raised issue with the timing of Cohen's testimony in a Monday appearance on Fox and Friends.

"Think about that, you've got a president trying to deal with a major world issue," Trump Jr. said. "And you know, to try to distract or whatever it is by bringing in a convicted felon and known liar. I mean it's pretty pathetic but it really shows you how much the Democrats hate Trump."

Cohen's lawyer Lanny Davis said in a statement to the New York Times, "These dates were developed over a long period of time, with lots of stops and starts and delays.

"We had to worry about being attacked with Trump tweets. Trump set up the first reason for the delay."

Asked last Friday if he was concerned about what Cohen might say in his testimony, Trump insisted he wasn't.

"No. No. No," Trump said. "It's lawyer-client, but, you know –-- he's taking his own chances."

ABC News' Conor Finnegan, Jordyn Phelps and Meridith McGraw contributed to this report.