Donald Trump has promoted a claim he will campaign for re-election on a message of “grievance, persecution and resentment” following his acquittal in the Senate of impeachment charges.

The US president’s comments came just minutes after he shared on Twitter a video of a US mayor being caught on a hot mic going to the toilet.

Quoting a two-week old New York Times article, Mr Trump tweeted: "Ralph Waldo Emerson seemed to foresee the lesson of the Senate Impeachment Trial of President Trump. ‘When you strike at the King, Emerson famously said, “you must kill him.’

"Mr. Trump’s foes struck at him but did not take him down. A triumphant Mr.Trump emerges from the biggest test of his presidency emboldened, ready to claim exoneration, and take his case of grievance, persecution and resentment to the campaign trail.”

Mr Trump then added, "The Greatest Witch Hunt In American History!" - a claim he has repeatedly made despite the fact 48 senators - including one Republican - voted to convict him over his attempts to pressure Ukraine into investigating his political rivals.

Moments earlier, the president had retweeted a post which showed a 2015 meeting in which the mayor of Georgetown, Texas, forgot to remove his microphone before heading for the bathroom.

The video showed an embarrassed colleague reacting to a series of noises played through speakers which were emanating from the bathroom cubicle.

The clip was posted by an anti-Trump twitter account alongside the caption: "THIS IS HILARIOUS. Mayor of Georgetown in the US excused himself to go & use the washroom in the middle of a meeting & forgot to switch off his mic on his tie & this is what happened."

Mr Trump's allusion to a grievance-based approach to his 2020 re-election campaign comes amid a concerted effort by the president to sow discord and suspicion among voters in the ongoing Democratic primaries.

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On Friday, Mr Trump tweeted: "It is happening again to Crazy Bernie, just like last time, only far more obvious. They are taking the Democrat Nomination away from him, and there’s very little he can do. A Rigged System!"

The president provided no evidence to support the claim Bernie Sanders, the frontrunner for the Democratic presidential nomination, will be denied a potential victory at the end of the process.

Later on Saturday, Mr Trump lashed out at Andrew McCabe, the former acting FBI director who was involved in the agency's early investigation into the Trump campaign's links with Russia.

It appeared to be prompted by a Justice Department decision earlier in the week to drop an investigation into Mr McCabe over a leak to the press.

"IG report on Andrew McCabe: Misled Investigators over roll in news media disclosure...Lacked Candor (Lied) on four separate occasions...Authotized Media Leaks to advance personal interests...IG RECOMMENDED MCCABE’S FIRING," Mr Trump said in reference to an inspector general report about the leak.