US president-elect Donald Trump has taken aim at his own Republican colleagues on the first day of the newly-elected Congress after they attempted to weaken an ethics watchdog.

The Republican Party moved to limit the powers of the Office of Congressional Ethics on Wednesday, but appeared to back down in the face of widespread criticism, including from Mr Trump.

“With all that Congress has to work on, do they really have to make the weakening of the Independent Ethics Watchdog, as unfair as it may be, their number one act and priority,” the President-elect posted on Twitter.

Mr Trump regularly used the phrase “drain the swamp” during his campaign, which was widely interpreted to mean removing corruption from Washington.

……..may be, their number one act and priority. Focus on tax reform, healthcare and so many other things of far greater importance! #DTS

— Donald J. Trump (@realDonaldTrump) January 3, 2017

Senator Chuck Schumer, the third-ranking Democrat in the upper house, tweeted in response that the US “cannot afford” the presidency to be run on social media.

“Our issues are too important for mere words. With all due respect, America cannot afford a #TwitterPresidency.”

University of Melbourne political expert Clayton Chin said Mr Trump’s attacks on his own party on the first sitting day were part of a bid to reaffirm his “outsider” status.

“The interesting thing is that while Trump’s intervention was brief … it wasn’t the substance of the proposals, it was the timing,” Dr Chin told The New Daily.

“He has to maintain arm’s length distance of the Congress because he wants maintain his outsider status.”

While Mr Trump criticised the timing, Democrats attacked the entirety of the attempt to gut the ethics watchdog, which was established in 2008 amid a string of political scandals, including the jailing of three US politicians.

“Who, exactly, thinks that the problem with Washington is that we have too many rules requiring the [government] to act ethically?” tweeted leading Democratic senator Elizabeth Warren.

Later on Wednesday (AEDT), after Mr Trump’s intervention and a flurry of protest from ethics groups and constituents, the Republicans appeared to back down.

“It was a stumble. Probably not the way you want to start out,” Republican Mark Sanford told The New York Times.

Republicans, defying their leader in Congress Paul Ryan, wanted to lessen the watchdog’s powers after it caused politicians to spend millions of dollars defending themselves against anonymous allegations.

Donald Trump will look to retain his outside status, experts say. Photo: Getty

Dr Chin said Mr Trump in future would be unable to attack Democrats because of the Republican majority in Congress, so he would likely use Twitter as a vehicle to differentiate himself.

Tweet storm

Ahead of his inauguration on January 20, Mr Trump has used Twitter to oppose plans to release prisoners from the US military jail at Guantánamo Bay and to warn North Korea over nuclear weapons.

On Wednesday, he also criticised intelligence authorities over a planned briefing to discuss alleged hacking during the US election.

The "Intelligence" briefing on so-called "Russian hacking" was delayed until Friday, perhaps more time needed to build a case. Very strange!

— Donald J. Trump (@realDonaldTrump) January 4, 2017

Earlier, he had picked a fight with General Motors, one of the world’s largest automakers.

General Motors is sending Mexican made model of Chevy Cruze to U.S. car dealers-tax free across border. Make in U.S.A.or pay big border tax!

— Donald J. Trump (@realDonaldTrump) January 3, 2017

Mr Trump was a frequent critic of the outsourcing of jobs as a result of free trade agreements, and has previously warned companies they could face export tariffs back into the US if they shift overseas.

General Motors challenged Mr Trump’s claim that the Chevy Cruze was made in Mexico.

JUST IN : GM says Chevy Cruze, which Trump earlier criticized for being "Mexican made" & sold "tax free across border", is made in Ohio. pic.twitter.com/oh66pKfdiB

— CNBC (@CNBC) January 3, 2017

But in a win for the incoming president, the Ford Motor Company said it would scrap plans for a new factory in Mexico, instead investing $US700 million ($A969 million) in Michigan.

Meanwhile, aides for Bill and Hillary Clinton confirmed the former first couple would attend Mr Trump’s inauguration, CNN reported.

Mr Trump also announced he would hold a general news conference in New York on January 11, his first since late July 2016.

The President-elect held an impromptu doorstop with reporters right before the new year, but has been criticised for restricting access to the media.