Something amazing has just happened in the US presidential election campaign.

Donald Trump, the Republican candidate, has said sorry.

This is a man who has, until now, carried out a verbal scorched-earth policy, leaving a trail of destruction in his wake as he takes on anyone who disagrees with him.

He likes to say he's just not politically correct, but that's a familiar refrain from people who use it to justify any kind of hate speech. No, Trump hasn't simply been politically incorrect; he's been downright offensive. Not just in his one-on-one battle with Democratic candidate Hillary Clinton but also during his earlier intra-party fight for the Republican nomination.

His erstwhile Republican rivals were called, amongst other things, ugly and liars. He has labelled Mexicans as rapists. He's had a public falling-out with the parents of a fallen Muslim US solider. He's gone on record to warn Clinton that she should be afraid of gun owners should she win in November (although he later claimed this was a joke). He has criticised the looks of an opponent's wife. And he has failed to condemn violence by his supporters against opponents at his rallies.

This hasn't all been good-natured political incorrectness. It's been extremely offensive (and often childish) behaviour from a man that a vast majority of Americans have come to realise is unfit to be their commander-in -chief.

So this apology, in which he said he 'regrets' any 'personal pain' he might have caused, is a huge change of course.

It's also strange timing, given recent developments within his senior campaign team. In yet another shake-up of Team Trump, he has just appointed a chap called Steve Bannon as his campaign chief. Bannon is from the Breitbart website, which has been in the tank for Trump since day one, and has manfully tried to defend even his most extreme proclamations.

Just one quick look at some of the rabid comments at the end of each story on that site highlights the sort of audience that website caters for.

It's easy to see why most observers thought that Bannon's appointment would see Trump become even more outspoken.

So far, though, this hasn't happened. We've had the apology, and now we'll see if Trump is serious about rolling back some of his more ridiculous/stupid/dangerous antics, and starting to portray a more presidential persona.

He certainly needs to do something. He is trailing in the polls nationally, and doing even worse in the battleground states where November's poll will be effectively won and lost. Clinton's leads in places such as Pennsylvania are starting to look unassailable.

This is no surprise, given Trump's efforts to alienate large swathes of the electorate. Hispanic and black voters overwhelmingly oppose him. Independents and women are also breaking heavily for Clinton. And there remains a sizeable chunk of the conservative movement who have rallied around the #nevertrump bandwagon, believing that he'll be responsible for the destruction of the Republican Party.

Some of those conservatives are also likely to vote for Clinton. Still more will vote for a third party or stay at home.

So new tactics have been needed for some time, and this apology is a good start.

However, his track record to date suggests he'll find it a tall order to maintain this new discipline. And with fewer than 80 days until the election, the feeling remains that it's all too little, too late, anyway.