The president suggested the House of Representatives Oversight Committee’s decision to interview his longtime fixer on the same day he met Kim Jong-un in Hanoi had been a factor in the two leaders’ failure to strike a deal.
He gave no explanation for how Mr Cohen’s testimony could have impacted on negotiations over Pyongyang’s nuclear programme.
Mr Trump tweeted on Sunday night: “For the Democrats to interview in open hearings a convicted liar & fraudster, at the same time as the very important Nuclear Summit with North Korea, is perhaps a new low in American politics and may have contributed to the ‘walk.’
He added: “Never done when a president is overseas. Shame!”
The president abruptly ended Thursday’s talks with Mr Kim, telling the media the North Korean leader had demanded “sanctions lifted in their entirety” in exchange for denuclearisation. He said in a subsequent press conference: "Sometimes you have to walk."
Hours earlier, Mr Cohen gave explosive public testimony in which he branded Mr Trump a “racist” and a “conman” who was involved in “criminal conspiracy”.
Asked about his former personal lawyer’s evidence at a press conference in Hanoi on Thursday, the president called the allegations “incorrect” and criticised the decision to hold the hearing while he was away.
“I tried to watch as much as I could,” Mr Trump said. “I wasn’t able to watch too much because I’ve been a little bit busy, but I think having a fake hearing like that and having it in the middle of this very important summit is really a terrible thing.”
Mr Cohen had originally been scheduled to testify to the committee on 7 February but cancelled his appearance, citing “threats against his family” he alleged had been made by Mr Trump and his lawyer Rudy Giuliani. The committee confirmed on 20 February that it had rescheduled the testimony for last week.
The president announced the date of his summit with Mr Kim on 5 February.
Republican senator Lindsey Graham last week accused Democrats of "undercutting an important foreign policy effort" by holding Mr Cohen's hearing on the same day as the North Korea talks.
North Korea has disputed Mr Trump's explanation for the breakdown of negotiations, saying it wanted only a partial lifting of sanctions in exchange for the dismantlement of its main nuclear facility.
Mr Cohen’s public testimony, in which he presented evidence Mr Trump was aware of illegal hush money payments to cover up affair allegations during the presidential campaign, was followed by behind-closed-doors grilling by two congressional panels investigating Russia’s interference in the 2016 election.