In a move widely denounced as a declaration of war on his own party, Donald Trump declared himself unbound by the "shackles" of the Republican Party leadership and free to run for the presidency – or, as he put it "to fight for America" – "the way I want to."

Mr. Trump's statement Tuesday morning was released, as usual, on Twitter and followed an announcement Monday by the United States' most powerful elected Republican – Speaker of the House Paul Ryan – who said he would neither campaign with nor defend Mr. Trump in the last four weeks of the presidential election.

Instead, Mr. Ryan said, he would put all his efforts into helping Republican candidates running for House and Senate seats in this election and urged every loyal Republican to do the same.

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This every-man-for-himself approach was brought on by the release last week of a misogynist video that showed Mr. Trump bragging about his impunity in sexually assaulting women. For many Republicans the video was the last straw and growing numbers of the party's elected members are distancing themselves from the Republican presidential nominee.

To which Mr. Trump replied with another tweet Tuesday: "Disloyal R's [Republicans] are far more difficult than Crooked Hillary. They come at you from all sides. They don't know how to win – I will teach them!"

Mr. Trump hinted darkly there may well be other salacious videos released that reveal more of the businessman's sordid nature, but that for every one that is released, he will launch further attacks on Democratic nominee Hillary Clinton and especially on her husband, former U.S. president Bill Clinton.

Long-time Republicans shudder at the prospect both of the revelations to come and of Mr. Trump's no-holds-barred form of fighting. Both could have long-term, detrimental effects on their party.

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But if turning against the party that nominated him for the presidency is the craziest thing Mr. Trump has done in this election, there are a number of other bizarre actions that could come a close second.

Throwing his running mate under the campaign bus

It happened during Sunday night's debate: Co-moderator Martha Raddatz had noted that Indiana Governor Mike Pence, Mr. Trump's choice for vice-president, had recently been critical of Russia for aiding in the Syrian government's deadly attacks on the besieged city of Aleppo.

Mr. Pence had gone so far as to say during a recent vice-presidential debate that the concerted attacks with Russia's participation might well justify the United States launching attacks on Syrian military targets.

Without blinking an eye, Mr. Trump dismissed Mr. Pence's position saying, "He and I haven't spoken, and I disagree."

It was an undignified way to treat a man who has been supremely loyal to Mr. Trump and whose performance in the VP debate was a credit to the Trump-Pence campaign.

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His pro-Russia stance

Not only has Mr. Trump declined to criticize Russian President Vladimir Putin for policies in Syria and for apparent cyberattacks on U.S. institutions, he has publicly praised Mr. Putin for being a stronger national leader than U.S. President Barack Obama and gushed about his popular support.

"Putin has an 82 per cent approval rating," Mr. Trump told Larry King last month.

His many lies

While Mr. Trump may play down vulgar behaviour as "locker-room talk," he probably minimizes his frequent falsehoods as colourful language.

Mr. Trump said he never supported the invasion of Iraq [he did]; he never said that Japan should have nuclear weapons [he did]. He said that Mr. Obama was the founder of the Islamic State terrorist organization; that he saw a video of pallets of U.S. money being handed over to Iran and another video showing Arab-Americans partying on the afternoon of Sept. 11, 2001.

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He made it all up.

His over-the-top behaviour

In his savage debate tactics and his tweeting from the hip, Mr. Trump is undoubtedly appealing to his base of supporters who hail largely from disadvantaged regions and sectors across the United States. To those who feel forgotten or ignored by "the system," Mr. Trump comes across as talking truth to power. His criticism of free-trade deals and illegal immigrants stealing jobs hits home. To them he is a hero, fighting for their America.

But by going too far, as he is now, he could well lose an election that many Americans think was eminently winnable, running against a Democrat with very low popular standing.