The first votes of the 2020 presidential cycle collide on Monday with President Donald Trump's impeachment trial, setting up an epic clash over presidential power and the direction of America.

After a brief respite over the weekend, senators will return to Washington to hear closing arguments from Democratic House impeachment managers and the President's legal defence team.

Hours later, and after months of exchanges on the campaign trail, Democratic voters finally begin their search for a candidate to make Trump a one-term President in Monday night's Iowa caucuses.

The commander-in-chief will hit back the next night, weaving a narrative of prosperity at home and strength abroad, as his re-election pitch reaches new intensity in his annual “State of the Union” address.

And then after finally breaking their own enforced silence with speeches from the floor, senators will on Wednesday undertake their gravest possible duty in voting on whether to make Trump the first impeached President to be ousted in US history. Spoiler: Republicans will ensure that Trump is acquitted of high crimes and misdemeanours and will leave it up to voters to decide his fate.

In its tumultuous national story, America has endured more consequential political earthquakes, including presidential assassinations, a Civil War brought on by slavery, epic conflicts abroad and the long march towards justice by the civil rights movement.

But it is unusual for three events with the potential to set the tone of a crucial campaign and the political year ahead to unfold in such a compressed time frame – one that encapsulates the sense-scrambling reality of Washington in the bewildering Trump era.

The next three days will reveal the political forces shaping the nation's present – like Trump's relentless dominance of the Republican Party and the desperation of Democrats to consign him to a single term. They will also unleash chain reactions that will shape the run-up to November's election and will reflect divisions widened by impeachment.

The identity of the next Democratic nominee and the way that the President behaves in the aftermath of his impeachment drama and up to and including the presidential election also have the possibility to set the country on one of several divergent courses.

A Democratic President like Joe Biden might seek to return to a more conventional, bipartisan style of leadership. A President Elizabeth Warren or Bernie Sanders could, however, take the country as far left as it has been in decades.

A second Trump term could prove just as challenging to the political establishment as his first and would give the President the chance to fundamentally reorder the state of national politics over two terms – especially with his appointment of conservative judges who are transforming American jurisprudence.

Bitter political battles

A fearsome day of the pitched political battle on Sunday emphasized the brittle political atmosphere and the still uncertain impact of impeachment on Democratic and Republican candidates in November.

Some Republicans reflected the pressure of their looming vote to acquit Trump despite an incriminating evidentiary record of his behaviour in Ukraine, offering veiled criticism of his conduct that could anger some GOP voters.

But one prominent Republican, however, appeared to signal a campaign of revenge against political foes who brought the President to this point. Democratic presidential candidates, especially senators who must return for the final stages of the Senate trial on Monday, made the most of the dying hours of the Iowa campaign.

And Trump appeared agitated by the possible threat posed by billionaire Democratic candidate Mike Bloomberg down the road. The former New York mayor was only too happy to join the exchange of insults, jumping at the chance to get into the mix, given that he's not even competing in the first four Democratic contests.

The President had the first shot at defining a critical week in politics during a softball Super Bowl pre-game network interview with one of his most vocal supporters, Sean Hannity of Fox News.

“There's a revolution going on in this country,” Trump said. “I made a positive revolution,” he added, expressing optimism about his reelection hopes.

Signs of Republican disquiet

The President has insisted all along that his pressure on Ukraine to dig dirt on former Vice President Joe Biden and his son Hunter and other Democrats – for which he was impeached by the House – was an example of “perfect” presidential behaviour.

But there were some signs on Sunday that Republican senators who will keep him from office are concerned about the electoral impact of shielding the President among uncommitted swing voters.

Several argued that though his conduct fell short of an impeachable standard, the President shouldn't have behaved in such a way, or may now have learned not to do so again.

Iowa Sen. Joni Ernst said on CNN's “State of the Union” that Trump pursued what she called corruption in Ukraine “in the wrong manner.” She added that his now-notorious conversation with Ukraine's President – in which he asked him to “do us a favour” – was “maybe not the perfect call.”

Trump's attempts to pressure Ukraine to investigate Hunter Biden and Joe Biden, his potential 2020 general election rival, are at the centre of the President's impeachment trial. Trump and his allies have repeatedly made unfounded and false claims to allege that the Bidens acted corruptly in Ukraine.

Republican Sen. Lamar Alexander of Tennessee is retiring so he doesn't have to face voters again but might have been conscious of history in explaining his planned vote to clear the President.

“I think he shouldn't have done it. I think it was wrong. Inappropriate was the way I'd say — improper, crossing the line,” Alexander said on NBC's “Meet the Press.”

But Alexander added: “I think what he did is a long way from treason, bribery, high crimes and misdemeanors. I don't think it's the kind of inappropriate action that the framers would expect the Senate to substitute its judgment for the people in picking a president.”

One of Trump's most enthusiastic supporters, Republican Sen. Lindsey Graham of South Carolina, warned that Republicans would start to investigate the Bidens and the intelligence community whistleblower who first raised the alarm about the President's conduct with Ukraine.

“We'll deal with the whistleblower … we'll deal with Joe Biden's conflicts of interest. (The) Judiciary Committee will deal with all things FISA,” Graham said on “Fox News Sunday.”

“Let me tell Republicans out there — you should expect us to do this. If we don't we're letting you down.”

The top House impeachment manager Rep. Adam Schiff argued meanwhile that signs of discomfort with the President's behavior from some of Graham's colleagues represented vindication for the Democrats’ impeachment tactics.

“You now have senators on both sides of the aisle admitting the House made its case. And the only question is, should the President be removed for office because he's been found guilty of these offenses?” Schiff said on CBS’ “Face the Nation.”

“I think it's enormously important that the country understand exactly what this President did. And we have proved it.”

Schiff would not say whether House Democrats would subpoena former national security adviser John Bolton who according to a New York Times report about his forthcoming book has evidence that incriminates the President in withholding military aid for Ukraine.

Last week, the Senate voted by a narrow margin to decline to hear testimony from Bolton and other witnesses, prompting Democratic accusations that the GOP-led chamb er was indulging in a coverup to save Trump.

Last chance in Iowa

Democratic candidates made their final pitches to Iowa voters ahead of caucuses on Monday night that could help set the tone for their nominating season.

Biden downplayed expectations in a state that is far less diverse than his typical coalition — but left enough space to capitalize on a victory.

“If we get out of Iowa with a win, I think It's going to be not clear sailing but overwhelmingly smooth sailing from here on,” he said in a call with precinct workers that CNN obtained access to. “But if we get out of here basically viewed as a tie with two or three people at the top of the ticket, I think we're clearly in the game.”

At and event in Cedar Rapids, Sanders all but predicted a win in a state where he came a narrow second to Hillary Clinton four years ago.

“We are the campaign of excitement and of energy,” Sanders said.