out Trump's attack on the family of Captain Humayun Khan, who was killed in action in Iraq

French President Francois Hollande said on Tuesday a victory by U.S. presidential candidate Donald Trump could make politics more conservative around the world and said the real estate magnate made people 'feel nauseous'.

A Trump victory in November could also affect France's presidential election in the spring of 2017, said Hollande, who has not yet announced if he will seek re-election.

'If the Americans choose Trump, that will have consequences, because an American election is a world election,' the Socialist leader told journalists.

The intervention by a world leader over the Capt Khan row came as President Barack Obama on Tuesday called Trump 'unfit' to become president.

'Yes. I think the Republican nominee is unfit to serve as president,' Obama said at a news conference, 'I said so last week and he keeps on proving it.'

Trump hit back claiming Obama, supported by Hillary Clinton in her time as Secretary of State, had 'destabilized the Middle East, handed Iraq, Libya and Syria to ISIS, and allowed our personnel to be slaughtered at Benghazi.'

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Speaking out: French president Francoise Hollande said of Trump: 'A certain number of excesses have ended up making people feel nauseous - even in the United States.'

Caught in a storm: Trump has become engulfed in days of difficulty over Captain Khan, whose father accused the Republican candidate of having a 'dark heart'

'It could lead to a very strong turn to the right in the world, or to a correction ... the American campaign shows issues that will be reflected in the French campaign,' said Hollande.

The Socialist will face strong competition from far-right National Front leader Marine Le Pen if he chooses to run again for the French presidency.

'A certain number of excesses have ended up making people feel nauseous - even in the United States - especially, as Donald Trump did, when criticizes the memory of a soldier,' he said.

Trump has been caught up in a row after the family of Captain Humayun Khan, killed in action in Iraq, spoke against him, with the officer's father, Khizr, speaking at the Democratic National Convention and accusing Trump of ignoring the constitution.

Trump questioned the silence at the event of the dead man's mother, Ghazala, prompting her to cry in a television interview and her husband to accuse Trump having a 'dark soul'.

Hollande said he was hearing 'hurtful, humiliating comments' during the election campaign. Speaking about politicians in general, he said 'they should be respected when they are respectable'.

Gold star family: Khizr Khan addressed the Democratic National Convention in Philadelphia last week flanked by his wife and accused Donald Trump of ignoring the constitution

Fallen: Captain Humayun Khan died in 2004 in a suicide attack on his base in Baqubah, telling his men to fall back as he ran towards a taxi which crashed through the gates. He is buried at Arlington National Cemetery

Obama said he was shocked by Trump's attack on the Khan family: 'The notion that he would attack a Gold Star family that had made such extraordinary sacrifices on behalf of our country. The fact that he doesn't appear to have basic knowledge around critical issues, in Europe, in the Middle East, in Asia means that he's woefully unprepared to do this job. '

Trump hit back with a statement in response to what he characterized as Obama's 'failed leadership.'

'Obama-Clinton have single-handedly destabilized the Middle East, handed Iraq, Libya and Syria to ISIS, and allowed our personnel to be slaughtered at Benghazi,' he said.

Jotting down all the areas of disagreement he shares with the president and Democrats' White House candidate, Trump said, 'Hillary Clinton has proven herself unfit to serve in any government office.'

The sitting president was afforded the opportunity to tear into Trump Tuesday afternoon at a joint press conference with the prime minister of Singapore when a reporter asked for his opinion on Trump's 'fitness' to succeed him.

Obama called on Republican leaders to disavow their party's nominee over his dispute with Khizr and Ghazala Khan.

He said doesn't doubt that Republicans are sincerely 'outraged' by Trump's comments, adding: 'But there has to come a point in which you say, somebody who makes those kinds of statements doesn't have the judgement, the temperament, the understanding to occupy the most powerful position in the world because a lot of people depend on the White House getting stuff right.'

President Barack Obama says he has serious doubts about Donald Trump's ability to serve as commander in chief

After his rally on Tuesday Trump responded to Obama with this scathing statement, seen above on his Facebook

The two-term president said his opposition to Trump replacing him at this point goes beyond policy differences, and he did not have these concerns about his 2008 and 2012 Republican opponents, John McCain and Mitt Romney.

'I didn't have a doubt that they could function as president,' he said. 'I think I was right and Mitt Romney and John McCain were wrong on certain policy issues, but I never thought that they couldn't do the job.'

If either of them had won, 'I would have been disappointed, but I would have said...to all Americans this is our president,' the Democrat stated.

Obama said he does not have the same confidence that Trump will 'abide by certain norms and rules and common sense' that go along with being president or that he would 'observe basic decency.'

'That’s not the situation here,' he professed. 'And this is not just my opinion, I think what's been interesting is the repeated denunciations of his statements by leading Republicans,' he said, that include Speaker of the House Paul Ryan and Senate Majority Leader and other prominent Republicans such as Senator McCain.

Eric Trump told CBS This Morning he believes his dad already has apologized by calling slain Army Captain Humayun Khan's family by calling him a hero

The president said 'the question that I think they have to ask themselves is, if you are repeatedly having to say in very strong terms that what he has said is unacceptable, why are you still endorsing him? What does this say about your party that this is your standard bearer?'

Meanwhile Trump's son Eric tried to pour water on the blazing row.

His father already has apologized to the family of slain U.S. Army Capt. Humayan Khan by calling him a 'hero,' Eric on 'CBS This Morning'.

He was asked about the demand by gold star families that the Republican presidential candidate apologize after tangling with Khan's parents, who appeared at the Democratic National Convention.

'Would your father be willing to apologize and move on?' asked co-host Norah O'Donnell.

'You know, that's a great question for him,' Eric Trump responded. 'And I think he has by calling him a hero,' he said.

He then tried to clean up his dad's statement on Sunday that he had sacrificed by building structures and employing thousands of people.

'You know, and in terms of the one question, whether you've made a sacrifice, I'm sure my father has. Now whether that's not the ultimate sacrifice – the ultimate sacrifice is a soldier dying for this nation, dying to protect the three of us, there's no question about it,' he told his interviewers.

'This was something that was honestly blown in, hugely, out of proportion,' because, first of all, he said that the Khan family looked like amazing people ... which for whatever reason never wants to get reported,' Eric Trump said.

'He called him a hero so many, so many different times ... this isn't a Muslim thing, this is an ISIS thing and also an anti-Syrian, anti-refugee thing coming into the country because he doesn't want to see more Americans dead. My father is a great patriot, he doesn't want to see more Americans dead, and he sees what's happening around the country, and quite frankly, he's shaking his head.'

There had been blowback from the controversy throughout Monday, as Arizona Senator John McCain blasted Trump for his remarks, the gold star families demanded an apology, and Khan's mother, Ghazala, gave a tearful interview on MSNBC.

Senate Majority Leader Mitch McConnell and House Speaker Paul Ryan both distanced themselves from Trump's comments.