Trump, interviewed by NBC News after a campaign appearance in Iowa on Thursday night, was asked if there should be a database to monitor Muslims in the United States.

“I would certainly implement that, absolutely,” he said. Asked how that differed from efforts last century to track Jews in Nazi Germany, and said: “You tell me.”

His comments came amid renewed security concerns following the Islamic State attacks in Paris last week that killed at least 129 people, and a political fight over U.S. plans to take in 10,000 refugees from Syria.

Two Republican presidential rivals, former Florida Governor Jeb Bush and Ohio Governor John Kasich, criticized Trump’s Muslim database proposal.

“That’s just wrong,” Bush said on CNBC on Friday.

“It’s manipulating people’s angst and their fears,” he said. “That’s not strength. That’s weakness.”

Kasich, whose Super PAC is launching a $2.5 million series of attacks against Trump, said the proposal proved the real estate mogul was not worthy of the White House.

“The idea that someone would have to register with the federal government because of their religion strikes against all that we have believed in our nation’s history,” Kasich said in a statement. “It is yet another example of trying to divide people, one against the other. Donald Trump is unable to unite and lead our country.”

Trump tied his database proposal to his immigration policy, which has become a central focus of his campaign for the Republican nomination in the November 2016 election.

Trump, who leads the Republican presidential field in opinion polls, has called for deporting the estimated 11 million illegal immigrants in America and building a large wall along the border with Mexico.

Trump, who earlier in the week called for shutting down American mosques, said Muslims would be legally required to register for the database and would be signed up “at different places.”

“There should be a lot of systems, beyond databases,” he said.

Democratic presidential front-runner Hillary Clinton also criticized Trump’s comments.

“This is shocking rhetoric. It should be denounced by all seeking to lead this country,” Clinton said on Twitter.

The Paris attacks have launched a growing debate on the 2016 campaign trail about the appropriate U.S. response.

As the debate over terrorism has gained prominence on the campaign trail, early polls show Republicans turning to Trump, a billionaire with no previous government experience, to tackle the issue. A Reuters/Ipsos poll taken in the days after the attack found 33 percent of Republicans think he is best suited to address terrorism, leading the field.

Ibrahim Hooper, spokesman for the Council on American-Islamic Relations, a Muslim rights group, said the rest of the Republican presidential field should say publicly whether they would close mosques, create a database of Muslims or require Muslims to carry a special ID card.

“This is way beyond the pale, this is basically a call to persecute a religious minority based on nothing other than their faith,” Hooper said.

The Paris attacks have also raised questions about U.S. plans to admit 10,000 refugees fleeing Syria’s civil war.

Many Republicans have called for a pause in the program because of fears that militants might sneak into the country. The Republican-led U.S. House of Representatives passed a bill on Thursday to halt Syrian refugees but President Barack Obama has vowed to veto it.

Other Republican presidential candidates have backed such efforts, including Trump’s closest Republican rival in the polls, retired neurosurgeon Ben Carson, who likened Syrian refugees to “rabid dogs” who would put the country at risk.