YOUNGSTOWN, Ohio — Donald Trump is calling for “extreme” vetting of immigrants seeking admission to the United States, but he’s offering few specifics about how that might work, how long it might last or how taxpayers would foot the bill.

Trump, who had previously called for an unprecedented temporary ban on immigration by Muslims, vowed Monday to overhaul the country’s screening process and block those who sympathize with extremist groups or don’t embrace American values.

“Those who do not believe in our Constitution, or who support bigotry and hatred, will not be admitted for immigration into our country,” Trump said in a foreign policy address in Youngstown, Ohio. “Only those who we expect to flourish in our country — and to embrace a tolerant American society — should be issued visas.”

The GOP presidential nominee has made stricter immigration measures a central part of his proposals for defeating the Islamic State — a battle he said Monday is akin to the struggle against communism during the Cold War. He called for parents, teachers and others to promote “American culture” and encouraged “assimilation.”

But he didn’t say which countries or regions would be subject to the “extreme” vetting, and his announcement that government agencies would create the list suggested that would not happen before the election in November.

The candidate’s aides said federal agencies would use questionnaires, social media, interviews with family and friends or other means to vet applicants’ stances on issues including religious freedom, gender equality and gay rights. Trump did not clarify how U.S. officials would assess the veracity of responses to the questionnaires or how much manpower it would require to complete such arduous vetting.