Sen. Mitt Romney (R-Utah) told CNN that he believes NATO members would have to "rethink" whether they can rely on the United States to defend other countries if former President Trump is re-elected.

Why it matters: Trump throughout his term repeatedly criticized NATO as one-sided and bad for America — even describing it as "obsolete" at one point — raising fears among European allies that he would either make U.S. involvement conditional or pull the country out of the defensive alliance altogether.

• NATO has significantly bolstered its troop presence on Europe's eastern flank in response to Russia's unprovoked invasion of Ukraine.

What they're saying: Romney told CNN that he believes Trump's "America first" foreign policy "frightens" other NATO members.

• "They wonder, 'Are we committed to NATO and to our mutual defense, or are we all going to go off on our own?'" Romney said.
• "They wonder if we are going to return to the policies that we've had for the last 70 years or, instead, if we're going to take the turn that Donald Trump represented," he added.
• "If he were to come back as the U.S. president, I think it would represent a pretty dramatic departure for the world, and they would rethink whether they can count on the United States to lead NATO to lead other nations as they push back against China and against Russia."

The big picture: Senior administration officials told the New York Times in 2019 that Trump had privately discussed a desire to pull the U.S. out of NATO several times over the course of 2018.

• Trump's former national security adviser John Bolton told the Washington Post this month that he thinks Trump would have done so if he won re-election in 2020.
• Overseas approval of the U.S. in NATO countries has also increased within the last year.

Go deeper: Pentagon to deploy six naval aircraft to Germany to bolster NATO