President Barack Obama said Tuesday he has serious doubts about Donald Trump's ability to serve as commander in chief and prominent Republicans should, too, after his latest gaffes.

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

Barking at the billionaire he said, '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 barked back with a statement that characterized as Obama's eight years in office as 'failed leadership.' He later said he'd go down as the 'worst president in history.'

'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.

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

'Yes. I think the Republican nominee is unfit to serve as president,' Obama said today at a news conference. 'I said so last week and he keeps on proving it.' Donald Trump is pictured above at a rally in Columbus Ohio yesterday

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.'

He said in an interview with ABC News' Washington, D.C. affiliate, ‘Well, he’s a terrible president. He’ll probably go down as the worst president in the history of our country. He’s been a total disaster.’

Trump also said he wasn't bothered by Obama maligning him. 'No, I think it just means he’s concerned that I’m gonna win,' he told ABC 7's Scott Thuman.

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.

Twice in one interview Trump made statements that have come back to haunt him, the first of which concerned a Muslim-American family that lost their son in Iraq, and the second involving Russia's incursion into Ukraine.

Obama called on Republican leaders to disavow their party's nominee over his dispute with Khizr and Ghazala Khan, the husband and wife that stood up to Trump at the Democratic convention.

He said doesn't doubt that Republicans are sincerely 'outraged' by Trump's comments,

'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,' he said, 'because a lot of people depend on the White House getting stuff right.'

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.

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

Obama said Trump's response to Gold Star family Khizr and Ghazala Khan's Democratic National Convention speech solidified his opinion that Trump doesn't have the necessary skills or temperament to be president

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?'

Obama pointed out that Republicans have had to denounce Trump's statements throughout the 2016 election with some regularity.

'This isn't a situation where you have an episodic gaffe, this is daily, and weekly, where they are distancing themselves from statements he's making,' he stated. 'There has to be a point in which you say, "This is not somebody I can support for President of the United States, even if he purports to be a member of my party." '

And 'the fact that that has not yet happen makes some of these denunciations ring hollow,' he said, adding, 'I don't doubt their sincerity, I don't doubt they are outraged about some of the statements that Mr. Trump and his supporters made about the Khan family.'

In his speech to the DNC Obama said he doesn't believe that Trump's views are reflective of the entire Republican Party. But when party leaders say silent, it 'effectively endorses and validates the positions that are being articulated by Mr. Trump.'

President Obama kisses a baby during the official welcoming ceremonies for Singapore Prime Minister Lee Hsien Loong on the South Lawn of the White House this today

Obama and PM Lee Hsien Loong review the troops during this morning's official welcoming ceremonies

President Barack Obama listens as Singapore Prime Minister Lee Hsien Loong makes his remarks during the official welcoming ceremonies

President Obama and Prime Minister Loong wave with their wives Mrs. Lee Hsien Loong (L) and Michele Obama from the White House balcony at the end of the ceremony

In the same interview with ABC News over the weekend that Trump suggested Mrs. Khan stayed silent at the DNC as her husband bashed him because her religion dictates that she be subservient to her spouse, he insisted Russia would not invade Ukraine.

Trump said of Russian President Vladimir Putin, 'He's not going into Ukraine, OK, just so you understand. He's not going to go into Ukraine, all right? You can mark it down. You can put it down. You can take it anywhere you want.'

'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 - President Obama on Donald Trump

ABC's George Stephanopoulos pointed out at the time that Russian-backed separatists have already siphoned off Crimea. For two years the U.S. has been working with Ukraine and the international community to get it back.

Trump replied, 'Well, he's there in a certain way. But I'm not there. You have Obama there. And frankly, that whole part of the world is a mess under Obama with all the strength that you're talking about and all of the power of NATO and all of this. In the meantime, he's going away. He takes Crimea.'

Obama did not delve into their disagreements about the North Atlantic Treaty Organization today, having publicly went to battle with Trump over the United States' leading role in the organization in the past.

He seemingly made reference to it, though, as he observed that Trump misunderstands 'critical issues' in Europe, the Middle East and Asia.

The statement about the Middle East was most likely a reference to Trump's claims that Obama's approach to the region resulted in the formation of ISIS, and his invitation to the Russians to put troops on the ground there.

As for Asia, the president was responding to Trump's assaults on the Trans-Pacific Partnership, a top-talker at the joint presser with the Singapore's Prime Minister Lee Hsien Loong.

Trump was holding a rally a short drive outside of Washington on Tuesday when Obama held his presser. At the rally, Lt. Col Louis Dorman gave him his Purple Star, seen above in Trump's hand

Trump was holding a rally a short drive outside of Washington on Tuesday when Obama held his presser.

The Republican nominee for president went on the attack after. He went beyond the areas Obama indirectly mentioned and he explained why he believes the president and his former secretary of state are he ones who are 'unfit' for the Oval.

He said they gave Iran a path to nuclear weapons and blamed them for the veterans affairs scandal.

'Hillary Clinton put the whole country at risk with her illegal email server, deleted evidence of her crime, and lied repeatedly about her conduct which endangered us all,' he proclaimed.

Trump also charged that Obama and Clinton 'released criminal aliens into our country who killed one innocent American after another -- like Sarah Root and Kate Steinle -- and have repeatedly admitted migrants later implicated in terrorism.'

'They have produced the worst recovery since the Great Depression. They have shipped millions of our best jobs overseas to appease their global special interests.

'They have betrayed our security and our workers, and Hillary Clinton has proven herself unfit to serve in any government office.'

Trump also brought up the 2012 terrorist attack in Benghazi, Libya, a topic that came up in Obama's news conference. The U.S. military yesterday launched its first airstrikes on ISIS there.

The reporter who inquired about Trump's fitness also asked Obama if he considers his failure to appropriately prepare for the aftermath of the 2011 intervention into the African country the 'worst mistake' of his presidency.

'Hillary Clinton has proven herself unfit to serve in any government office,' Donald Trump

Obama said, 'With respect to Libya, I have said on several occasions that we did the right thing in preventing what could have been a massacre, a blood bath in Libya. And we did so as part of an international coalition and under U.N. mandate.

'But I think that all of us, collectively, were not sufficiently attentive to what had to happen the day after, and the day after, and the day after that, in order to ensure that there were strong structures in place to assure basic security and peace inside of Libya.'

Another question dealt with trade.

Neither Clinton nor Trump back the president's trade because of the implications they say it has for Americans workers and jobs in the homeland.

Obama told a questioner who asked about the future of the accord under either a Clinton or a Trump administration as neither of them agree with it as written, 'Well right now I'm president. And I'm for it.'

'I've made this argument before, I'll make it again. We are part of a global economy. We're not reversing that. It can't be reversed, because it is driven by technology, and it is driven by travel and cargo containers, and the fact that the demand for products inside of our country means we gotta get some things from other places,' he said.

Defending his 12 nation accord that is yet to get the approval of Congress, Obama said 'the notion that we're gonna pull that up root and branch is unrealistic.'

FITNESS TEST: After Obama said Trump's unfit to be president, Trump said his Democratic opponent, Hillary Clinton, above yesterday in Nebraska, is the one who is unfit for office

Opposition to the Pacific Rim deal is primarily coming from within Obama's own party in Congress.

The president acknowledged the uncomfortable intra-party dispute today, saying, 'I’ve got some very close friends, people I admire a lot, but who I just disagree with them.

WHO ME? Russian President Vladimir Putin also came up in the context of the DNC meail hack. Obama said, 'If, in fact, Russia engaged in this activity, it’s just one on a long list of issues that me and Mr. Putin talk about...'

'And that’s okay. I respect the arguments that they’re making. They’re coming from a sincere concern about the position or workers and wages in this country.,' he said. ut I think I’ve got the better argument, and I’ve got the evidence to support it.

And hopefully, after the election is over and the dust settles, there will be more attention to the actual facts behind the deal and it won’t just be a political symbol or a political football. And I will actually sit down with people on both sides, on the right and on the left. I’ll sit down publicly with them and we’ll go through the whole provisions. I would enjoy that, because there’s a lot of misinformation.

'But I think I've got the better argument, and I've got the evidence to support it,' he said Tuesday. 'And hopefully, after the election is over and the dust settles, there will be attention to the actual facts behind the deal and it won’t just be a political symbol or a political football.'

He said in his opening remarks the trade deal will reduce tariffs basically on American products and make it easier for Americans to export goods 'into the fastest-growing markets of the world.

'TPP levels the playing field for our workers and helps to ensure countries abide by strong labor and environmental rules,' he said. 'So this is an opportunity to grow our economies and write the rules for trade in the 21st century in a way that's equitable.

Speaking to the concerns progressives within his party have, he said, 'It gives us a chance to advance American leadership, reduce economic inequality, and support good-paying jobs -- all while strengthening critical strategic relationships in a vital region.'

Obama and Long held a bilateral meeting today to discuss the president's trade deal

Democrats are demanding that the accord not come up for a vote during the so-called lame duck period between the election and the inauguration.

Obama committed today to sitting down with people on both sides of the aisle before the vote and going over it publicly.

'I would enjoy that,' he said.

Even though the GOP nominee, the Democratic nominee and the bulk of Democrats are fighting it, Obama predicted he'd get it approved. 'People said we weren't going to be able to get trade authority,' he said, invoking the fast-track agreement that gave him the power to unilaterally negotiate it, 'to even present this before Congress, and somehow we muddled through and got it done.'

'And I intend to do the same with respect to the actual agreement,' he said.

The president also addressed the hack on the Democratic National Committee's emails, purportedly at the hands of Russians acting on behalf of the foreign country's government.

After Hillary Clinton campaign latched onto those reports and using them as the basis for claims that the Russians want Trump to win the election, Obama said it was possible Vladimir Putin was involved.

Today he said, 'If, in fact, Russia engaged in this activity, it’s just one on a long list of issues that me and Mr. Putin talk about and that I’ve got a real problem with.

'And so I don’t think that it wildly swings what is a tough, difficult relationship that we have with Russia right now,' he said. But it’s not going to stop us from still trying to pursue solutions so that we can, for example, implement the Minsk Agreement and get Russia and those separatists to lay down arms and stop bullying Ukraine.