President Obama slammed Republican nominee Donald Trump as “unfit” and “woefully unprepared” to be president during a news conference with Singapore’s prime minister at the White House. Pablo Martinez Monsivais/AP

President Obama reiterated that he believes Donald Trump is “unfit” to be president, issuing a sharp rebuke of the Republican nominee from the White House East Room Tuesday.

“Yes, I think the Republican nominee is unfit to be serve as president,” Obama said in response to a question from a reporter during a news conference with Lee Hsien Loong, the prime minister of Singapore. “I said so last week, and he keeps on proving it.”

Obama’s reference to last week was during his speech at the Democratic National Convention in Philadelphia, where Hillary Clinton, Obama’s former secretary of state, was nominated to be the Democratic nominee.

Obama then pivoted to question why Republican leaders, who have denounced Trump’s response to a handful of issues. The latest being Trump’s flap with the Khan family, the parents of former Army Capt. Humayun Khan, who was killed in Iraq in 2004. Khizr Khan, Humayun’s father, criticized Trump at the Democratic convention, questioning if Trump had read the Constitution and charging that the New York real-estate developer had sacrificed little.

“[T]he 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 in particular of Republican leaders like House Speaker Paul Ryan, Senate Majority Leader Mitch McConnell and 2008 nominee and Arizona Sen. John McCain.

“What does this say about your party that this is your standard-bearer?” Obama continued. “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. There has to be a point at which you say, this isn’t somebody I can support to be president of the United States, even if he purports to be a member of my party. The fact that this has not happened makes these denunciations ring hollow.”

During the GOP primary, Trump was critical of McCain and casting doubt on his status as a war hero. “He’s a war hero, ’cause he was captured,” Trump said of McCain. “I like people that weren’t captured, OK?”

Obama said he doesn’t doubt that leaders like Ryan, McConnell and McCain were “outraged” by Trump’s reaction to the Khan family. “But there has to be a point where you say, ‘Someone who makes that kinds of statements doesn’t have the judgment, the temperament, or the understanding to occupy the most powerful position in the world.’ Because a lot of people depend on the White House getting stuff right.”

Obama added that his criticism is more fundamental than policy differences. “I recognize [the Republicans] profoundly disagree with myself and Hilly Clinton on tax policy or certain elements of foreign policy. But there have been Republican presidents with whom I disagreed with, but I didn’t have a doubt they could function as president. I think I was right and Mitt Romney and John McCain were wrong on certain policy issues, but I never thought they couldn’t do the job….

“But that’s not the situation here. … There has to come a point at which you say, ‘Enough.’ The alternative is that the entire Republican Party effectively endorses and validates the positions being articulated by Mr. Trump.”

As of Tuesday afternoon, Trump had not yet responded.