Gregory Korte

USA TODAY

WASHINGTON — President Obama declared Donald Trump unfit for office on Tuesday, calling on Republicans to distance themselves from their party's presidential nominee.

"Yes, I think the Republican nominee is unfit to serve as president," Obama said Tuesday at a press conference with the prime minister of Singapore. "I said so last week, and he keeps on proving it."

"The notion that he would attack a Gold Star family that has 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."

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Obama lauded Gold Star families in a speech to disabled veterans on Monday. Although he did not mention Trump by name then, his remarks were clearly understood as a response to Trump's ongoing feud with Khizr Khan, whose son was killed in the Iraq war in 2004 and who denounced Trump at the Democratic National Convention last week.

Obama's comments Tuesday were more specific, but delivered in a more dispassionate tone than his own convention speech endorsing Trump's Democratic rival, Hillary Clinton.

In that speech, Obama argued that Trump's own convention "wasn’t particularly Republican — and it sure wasn’t conservative." On Tuesday, he took that argument a step further, saying Republican denunciations of Trump's more bombastic statements "ring hollow" from GOP leaders who continue to support his candidacy — notably House Speaker Paul Ryan, Senate Majority Leader Mitch McConnell, and Arizona Sen. John McCain.

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"The question 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?" Obama said. "What does this say about your party that this is your standard-bearer? This isn't a situation where you have an episodic gaffe. This is daily and weekly, where they are distancing themselves from statements he is making."

Obama said it's not an argument he would have made about his former rivals. "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."

Trump responded with an e-mailed statement on Obama's "failed leadership," saying Obama and Clinton "destabilized the Middle East, handed Iraq, Libya and Syria to ISIS, and allowed our personnel to be slaughtered at Benghazi."

The president's remarks on Trump were also notable in that they came during a joint press conference with a foreign leader, Singapore Prime Minister Lee Hsien Loong.

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For his part, Lee largely demurred about a question about U.S. politics, saying, "I don't think this is the right forum — or indeed, there is any right forum for me to talk about U.S. politics in public at this moment."

But he did say the relationship between the two countries would likely continue. "After the elections, in a calmer, cooler atmosphere, positions are rethought, strategies are nuanced, and a certain balance is kept in the direction of the ship of state. It does not turn completely upside down," he said.

"The Americans take pride in having a system with checks and balances. So, it is not so easy to do things, but it is not so easy to completely mess things up," Lee said. "We admire that, and sometimes we depend upon that."

"He's absolutely right," Obama replied, smiling. "The wisdom of our founders."