Washington, London-U.S. President Barack Obama attacked Republican presidency candidate Donald Trump on Tuesday and described him as “unfit” to become a president.

In a press conference held in Washington with Prime Minister of Singapore Lee Hsien Loong, Obama called on Republican Party leaders to disown him. “He keeps proving it,” said Obama.

Obama’s comments came amid a roiling war of words between Trump and the Muslim family whose U.S. Army captain son was killed in Iraq in 2004 as Trump rebuked the Republican nominee as having “sacrificed nothing.”

Families who lose an immediate relative in a U.S. military action are called Gold Star families.

“The notion that he would attack a Gold Star family that made 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 is woefully unprepared to do this job,” said Obama.

Obama turned up the heat on Republicans who appear increasingly ill at ease with Trump but have not withdrawn their endorsement.

“This isn’t a situation where you have an episodic gaffe,” Obama said. “This is daily and weekly where they are distancing themselves from statements he’s making.”

“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.’”

“There has to come a point at which you say ‘enough,’” he said.

Obama noted that leading Republicans, including Speaker of the House of Representatives Paul Ryan, Senate Republican leader Mitch McConnell, and one-time Republican presidential nominee John McCain, a U.S. senator from Arizona, had criticized Trump for his remarks but have stood by their endorsements of him.

Senator McCain from Arizona, a leading voice on military matters in Congress said: “While our party has bestowed upon him the nomination, it is not accompanied by unfettered license to defame those who are the best among us.”

Moreover, Obama, speaking at a Disabled American Veterans conference in Georgia on Monday, tore into those “trash-talking” the U.S. military and disrespecting the families of fallen soldiers, in a thinly veiled attack on Trump.

“No one has given more for our freedom and our security than our Gold Star families,” he said.

“Our Gold Star families have made a sacrifice that most of us cannot even begin to imagine.”

“We have to do everything we can for those families and honor them and be humbled by them,” Obama added.