US election 2016: Donald Trump's unwise battles - or were they?

Donald Trump's renewed attack on Venezuelan-born former beauty pageant queen Alicia Machado is prompting many to ask - why is he doing it?

It appears to be the latest example of the Republican candidate digging a hole for himself from which it may be difficult to emerge with much dignity.

That said, previous attacks on women and foreigners have done little to derail his campaign to become US president.

Here are some of the stranger fights Mr Trump has picked, and how they turned out.

Megyn Kelly moderated a TV debate last August, when Mr Trump was just one of many contenders for the Republican nomination.

She challenged him on his views about women, saying: "You've called women you don't like fat pigs, dogs, slobs and disgusting animals." He responded by saying: "I don't have time for total political correctness."

That was the beginning of a nine-month battle.

Afterwards he told reporters Ms Kelly had been "unfair" before launching a broadside on Twitter, saying she was a "bimbo" and had "really bombed".

Mr Trump then took things to a whole new level. Calling in to CNN, he suggested Ms Kelly had been tough on him because she was menstruating.

"You could see there was blood coming out of her eyes. Blood coming out of her - wherever," he said.

Mr Trump's top political adviser Roger Stone left the campaign as a result, tweeting that the Republican "didn't fire me - I fired Trump". Mr Trump was also disinvited from a major conservative conference - and Ms Kelly was invited in his place.

In September, Mr Trump launched a short-lived boycott of Fox News and in January refused to appear on a TV debate Ms Kelly was hosting. He told media outlets he "didn't like" Ms Kelly and thought she was a "third-rate reporter".

During the January debate, Ms Kelly called him the "elephant not in the room".

In May, Mr Trump was interviewed by Ms Kelly and apologised - "Did I say that? Excuse me" - for calling her a bimbo.

But he also insisted that he would not have been in pole position for the Republican nomination had he behaved in a "soft" and "presidential" manner.

Draw. Ms Kelly won the battle but Mr Trump stayed on course for the Republican nomination.

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In July, Khizr Khan, father of a US Muslim soldier killed in action in Iraq, told the Democratic convention that Mr Trump was "smearing the character of Muslims", questioned whether he had read the US Constitution and said he had "sacrificed nothing" for his country.

Mr Trump had earlier pledged to ban Muslims from entering the US.

The Republican hit back by saying Mr Khan had "no right" to criticise him and suggesting that Mr Khan's wife Ghazala had been forbidden to speak because of her religion - "She had nothing to say, maybe she wasn't allowed to have anything to say, you tell me," he told ABC.

The attack on "Gold Star parents" - those who have lost a child in war - sparked outrage across the political spectrum.

Mr Trump's former rival for the nomination, Ohio Governor John Kasich, tweeted that there was "only one way to talk about Gold Star parents: with honour and respect"; Senator John McCain said Mr Trump did not have an "unfettered licence to defame those who are the best among us".

Mr Trump attempted to calm the situation, saying Captain Khan had been a "hero" killed by "radical Islamic terror".

Twitter users also weighed in, mocking Mr Trump's claim that creating jobs equated to making a sacrifice for the country under the hashtag #TrumpSacrifices, listing such hardships as flying commercial class and playing on a municipal golf course.

As the feud continued, the Khans and Mr Trump carried on bashing each other in media interviews - despite the best efforts of Mr Trump's staff to rein him in, according to the New York Times.

Mrs Khan said she had not addressed the Democratic Convention because she was still overwhelmed with grief, while her husband said Mr Trump's "ignorance" had amazed him.

For his part, Mr Trump said he had no regrets about clashing with the Khans and moved into open conflict with those Republicans who had criticised him.

Draw. Mocking the Gold Star parents was a taboo too far, but powerful Republicans were unable to use the row to bring the Trump campaign down.

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In June, Mr Trump suggested that Gonzalo Curiel, a US-born judge born to Mexican migrants who was presiding over a fraud case against the now defunct Trump University, would be biased against him because of his ethnicity.

"We're building a wall," Mr Trump said. "He's a Mexican."

He called for the judge to withdraw from the case

The comments caught members of the Republican establishment flat-footed.

House Speaker Paul Ryan, who had just endorsed Mr Trump, accused him of "textbook racism" and said he should take the comments back.

Mr Trump said his comments had been "misconstrued" as a broad attack on people of Mexican heritage.

He also said it was possible a Muslim judge might be similarly biased against him because of his call for a ban on Muslims entering the country.

Draw. Judge Curiel continued to preside over the Trump University case, but Republicans continued to back Mr Trump as their candidate.

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