Former Texas Rep. Beto O'Rourke said Sunday that Donald Trump 'has yet to be brought to justice' for 'potential crimes' he committed during the 2016 campaign and in the years since.

On ABC's 'This Week' program, the onetime U.S. Senate candidate and current White House hopeful agreed with House Speaker Nancy Pelosi's now infamous contention that the president belongs 'in prison.'

Asked if Trump commited crimes, O'Rourke responded that 'he did,' and claimed 'those crimes might extend beyond what we've seen in the Mueller report.'

Former special counsel Robert Mueller's report to the attorney general this spring concluded that Trump's campaign did not collude with Russian agents to win the 2016 election.

AG Bill Barr and his deputy, Rod Rosenstein, jointly determined that charging the president with obstruction of justice couldn't be supported based on the evidence Mueller collected over the space of nearly two years.

Former Texas Democratic congressman Beto O'Rourke said Sunday that Donald Trump should be pursued by criminal investigations and 'brought to justice' for 'potential crimes'

Former special counsel Robert Mueller's final report to the attorney general cleared Trump of allegations that his campaign colluded with Russia, but an ambiguous case for obstruction of justice has given Democrats plenty of read mead to chew on

But O'Rourke, one of just three Democratic 2020 candidates to appear on the Sunday political talk shows, took the opportunity to call for more than an impeachment.

'I would want my Justice Department, any future administration’s Justice Department to follow the facts and the truth and to make sure at the end of the day that there is accountability and justice,' he said.

'Without that, this idea, this experiment of American Democracy, comes to a close.'

'We were attacked unlike any other time in our 243 year history. And we have a president who has yet to acknowledge it and a president who has yet to be brought to justice. So yes, at the end of the day, justice is important,' he said.

He also said a vigorous impeachment process should be on Demcorats' radar screens.

'Regardless of the popularity of the idea or what the polling shows us, we must proceed with impeachment so that we get the facts and the truth and at the end of the day there is justice for what was done to our Democracy in 2016 and the other potential crimes that this president has committed.

O'Rourke is slipping in the polls; Saturday's numbers from Iowa show him with just 2 per cent, comparde with 6 per cent who chose 'none of these' when presented with a list of Democrats running for president

Democrats could impeach Trump with a simple-majority vote in the House, but Pelosi has resisted calls from members on the left flank of her caucus to pursue that option.

The Republucan-led U.S. Senate would not be expected to remove Trump from office, but would be obliged to hold a public trial.

Public polls show a lack of support for impeachment but most of Trump's democratic rivals have said they support the move.

So far there has been no indication that Trump could face a criminal charge for anything arising from the Mueller probe.

O'Rourke, once seen as a liberal wunderkind, has seen his campaign largely fizzle. According to an average maintained by Real Clear Politis, he has the support of 3.8 per cent of Democrats.

A ground-shaking poll of Iowans released Saturday by the Des Moines Register and CNN put O'Rourke at just 2 per cent despite a sustained campaign in the Hawkeye State, down from 11 per cent in December.

'I don't know that this many months out from the caucuses in Iowa these polls really indicate what our prospects are,' O'Rourke said on 'This Week.'

'If I relied on polls in any race I've run, I never would have served in the U.S. Congress, never would have taken on Ted Cruz. Never would have been able to lead the largest grassroots effort in the state of Texas.'