NEW YORK (AFP) -- As a candidate one of the ways Donald Trump shocked America was by locking horns nastily with anybody who got in his way.

He once mocked a journalist with a disability. He argued for a couple of days with the Pakistani-born parents of an Army captain who was killed in Iraq.

Now, Trump is days away from being sworn in as president and little has changed: he dwells on minutiae far removed from things presidential and spends a lot of time settling scores.

Before breakfast on Friday, Trump took aim at Arnold Schwarzenegger, the new host of "Celebrity Apprentice", because the reality TV show's ratings are lower than when Trump was its star until 2015.

"Wow, the ratings are in and Arnold Schwarzenegger got 'swamped' (or destroyed) by comparison to the ratings machine, DJT," Trump wrote on Twitter, his main conduit for communicating.

"But who cares, he supported Kasich & Hillary," he added in a second tweet, referring to a former rival in the Republican primaries and to Hillary Clinton, whom he defeated in the November election.

The ratings plunge -- 21 percent compared to the first episode of the 14th season of the show, Trump's last -- was not news until Trump decided it should be.

And in blasting Schwarzenegger along the way, Trump effectively attacked a show in which he himself is still executive producer, at the risk of sapping revenue of which he is a beneficiary.

The Republican billionaire has attacked the New York Times and Vanity Fair magazine, arguing wrongly that their circulations were down.

He has also fired away, among others, at the comedy show "Saturday Night Live," in which actor Alec Baldwin lampoons him, and CNN. The list goes on.

Trump seems tireless.

"People said that after he got elected he would act more presidential, that he would change as he assumes the role of the office," said Daniel Kreiss, associate professor at the University of North Carolina School of Media and Journalism.

"And yet here we are months into the transition and Trump hasn't changed one bit," Kreiss added. "I have no reason to suspect that it will change."

His sawed-off-shotgun approach to expressing his opinion may have a down side in what Americans think of Trump, said David Lewis, a professor of political science at Vanderbilt University.

"The fact that the president-elect gives opinions about subjects that have very little to do with politics, that can affect their opinions of him," Lewis argued.

"I think there's a real danger here of him sort of being overexposed in ways that get fatiguing and make people less receptive to his approach domestically," he added.

Politicians generally are very careful about how and how often they say things publicly so as to protect the impact of their message, Lewis said.

Before Trump, Barack Obama was without a doubt the first president of the social media area. Since 2007 he has tweeted more than 15,000 times -- an average of more than four a day.

But Obama has a team of professionals do this, and it is rare for him to tweet himself, said Kreiss.

What is more, Trump's tone in his tweets could not be more different from Obama's. It is often aggressive, angry and personal.

Exclamation points and capital letters abound. His acidic wording regularly goes far, far beyond what is traditional for US politicians.

Trump regularly dismisses the US media as being "dishonest." Just this week he derided the Senate's top Democrat, Chuck Schumer, as a "clown." This came just weeks after he praised Schumer as being "much smarter" than his predecessor, Harry Reid. Trump complained of fraud before and after the election, when there was no evidence of this.

"It just doesn't seem in his nature to really think harder what it is he's putting out there and why," said Kreiss.

He said you can see this also in Trump's seemingly cavalier approach toward possible conflicts of interest between his business empire and his job as president.

"In nearly every single measure, Trump is undermining democratic norms and democratic institutions here in the United States," said Kreiss.

For this reason, he said, some of Trump's tweets are more worrisome than the ones that have zero to do with being president.

Trump's filter-free way of speaking, especially on social media, was popular with voters but there is a lot more at stake when the whole world is listening, as will be the case from now on.

"The risks of loose talk are particularly high in foreign policy and the president-elect doesn't seem to mind taking those risks," said Lewis.