In his strongest attack yet on Donald Trump, former FBI Director James Comey said the Democrats “must win” in 2020 to end his presidency.

“All of us should use every breath we have to make sure the lies stop on January 20, 2021,” Mr Comey told an audience at a public event in New York City on Sunday night.

The former FBI has become an outspoken critic of Mr Trump since he was fired by the president in May 2017. Although he stopped short of backing impeachment proceedings, Mr Comey said he desperately wanted to see a “landslide” victory for Mr Trump’s opponent at the next presidential election.

“I understand the Democrats have important debates now over who their candidate should be, but they have to win. They have to win,” he told MSNBC’s Nicolle Wallace at the 92nd Street Y discussion.

Mr Comey said voting against Mr Trump at the ballot box would “rid ourselves of this attack on our values … Removal by impeachment would muddy that.”

The former law enforcement official also claimed the president was “certainly close” to being named as an unindicted co-conspirator in some of the charges made against Trump associates by special counsel Robert Mueller.

It follows the stunning court filings released on Friday in which federal prosecutors alleged Mr Trump ordered his former attorney Michael Cohen to make illegal payments to two women in exchange for silence on sexual encounters.

When asked what usually happened after such a filing, Mr Comey said: “That person would be in serious jeopardy of being charged.”

California’s Democratic congressman Adam Schiff, incoming chair of the House Intelligence Committee, said prosecutors may seek to indict Mr Trump on charges related to the alleged illegal payments as soon as he leaves office.

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“There’s a very real prospect that on the day Donald Trump leaves office, the Justice Department may indict him – that he may be the first president in quite some time to face the very real prospect of jail time,” Mr Schiff told CBS’s Face the Nation.

Mr Comey testified before the House Judiciary and Oversight and Government Reform committee about his own 2016 probe into Russian election meddling on Friday.

On Sunday, Mr Trump accused the former FBI boss of lying to congressional officials. “Leakin’ James Comey must have set a record for who lied the most to Congress in one day. His Friday testimony was so untruthful!” Trump tweeted.

At the event on Sunday evening, Mr Comey reminisced about the less chaotic leadership style of former president Barack Obama.

“I was struck that Barack Obama is the best listener as a leader I had ever seen and Donald Trump is the worst I’ve ever seen,” he said.