President Barack Obama lit into Donald Trump again on Tuesday, this time attacking the Republican presidential nominee for slandering a Muslim family whose son was killed while fighting in Iraq.

He added that Trump lacks "basic knowledge" about "critical issues," and that he believes he doesn’t have "the judgment, the temperament, or the understanding to occupy the most powerful position in the world."

"I think the Republican nominee is unfit to serve as president," Obama said, while speaking next to the Singaporean prime minister at a press conference. "I said so last week, and he keeps on proving it. 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."

Most of the coverage of Obama’s remarks focused on his hit on Trump. But his comments were primarily an appeal to top Republican leadership, which has tried to criticize Trump’s most offensive statements while also still supporting him over Hillary Clinton in the election.

That position, the president argued, is becoming increasingly impossible to hold.

"There has to come a point at which you say, ‘This is not somebody I support for president of the United States, even if he purports to be a member of my party,’" Obama said. "The fact that this has not happened makes these denunciations ring hollow."

Vox’s Dylan Matthews explained yesterday just why it’s so hard for congressional Republicans to bring themselves to endorse Clinton, even while they condemn what Trump is doing.

But Obama has now made clear that he doesn’t have much sympathy for that argument. Here’s what he went on to say: