President Barack Obama launched his harshest attack to date on Republican presidential nominee Donald Trump, declaring him “unfit” and “woefully unprepared” to hold the office, and calling on the GOP leaders to withdraw support from the candidate.

The president made the remarks Tuesday, during a White House news conference with Lee Hsien Loong, the prime minister of Singapore, who is on a state visit to Washington.

“The Republican nominee is unfit to serve as president,” Obama said. “He keeps on proving it.”

Read more

“The notion that he would attack a Gold Star family that made such extraordinary sacrifices on behalf of our country, the fact that he doesn't appear to have basic knowledge of critical issues in Europe, the Middle East, in Asia, means that he's woefully unprepared to do this job,” the president added.

He was referring to Trump’s comments that he was “viciously attacked” by Khizr and Gazala Khan, whose son died in Iraq while serving as a captain in the US Army. The Khans spoke last week at the Democratic National Convention in Philadelphia, Pennsylvania, where they endorsed Hillary Clinton’s presidential candidacy.

Obama, who spoke in Philadelphia a day before the Khans and gave a ringing endorsement of Clinton, said that Republicans should withdraw support from Trump on account of his behavior.

“What does this say about your party that this is your standard-bearer?” he asked, addressing the question to Speaker of the House Paul Ryan (R-Wisconsin), Senate Majority Leader Mitch McConnell (R-Kentucky) and Senator John McCain (R-Arizona), who have all criticized Trump’s remarks over the past week.

“I don't doubt their sincerity. I don't doubt they were outraged by some of the statements that Mr. Trump and his supporters made about the Khan family,” Obama said. “But there has to come a point in which you say, 'Somebody who makes those kinds of statements doesn't have the judgment, the temperament, the understanding to occupy the most powerful position in the world’.”

Obama: Withdraw your support for a guy who insulted a man whose son died in a pointless war so a woman who voted for it can be president — J. Arthur Bloom (@j_arthur_bloom) August 2, 2016

“This isn't a situation where you have an episodic gaffe,” he added. “This is daily and weekly where they are distancing themselves from statements he's making. There has to be a point at 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’.”

“Unfit” has been the insult of choice for the Democrats to describe the billionaire businessman who trounced the GOP establishment to capture the nomination. Just hours before Obama’s comments, the same phrase was used by Representative Richard Hanna (R-New York), who announced his endorsement of Hillary Clinton.

Trump himself called Clinton “unfit for office” in a tweet last week during her keynote speech at the DNC, arguing that the former secretary of state was responsible for Islamic State and wars across the Middle East.