South Bend Mayor Pete Buttigieg took a firm stance on candidates accepting election help from foreign actors, saying candidates should immediately alert the FBI if offered dirt on their opponents. "Just call the FBI. It's not hard. It's not complicated," Buttigieg told "Face the Nation" host Margaret Brennan in an interview.

Buttigieg condemned President Trump for saying in an interview with ABC News' George Stephanopoulos that he would accept election help from foreign countries and would not necessarily report it to the FBI. Mr. Trump said accepting foreign help is "not an interference" and that FBI Director Christopher Wray was "wrong" for saying candidates should immediately contact his agency in such cases.

Buttigieg disagreed with Mr. Trump, saying accepting foreign help was indeed "foreign interference in American politics."

"And by the way, this isn't hypothetical. This isn't theoretical," Buttigieg said, referring to the conclusion by U.S. intelligence and Special Counsel Robert Mueller that Russia interfered in the 2016 presidential elections with the goal of aiding Mr. Trump.

"We were attacked by a hostile foreign power that decided that they could damage America, destabilize America, by intervening in the election to help him win. And they did and he did, and now America's destabilized," Buttigieg continued. "So, this is not some academic exercise. This is something that has happened and will probably happen again."

Buttigieg also took a shot at Mr. Trump's oft-repeated promise that his administration would put "America first," saying that a president who truly prioritized the American people would not accept foreign election help.

"If you believe in putting this country first, how could you ever talk about allowing a foreign — potentially hostile foreign power to interfere in the most sacred thing that we have in our civic tradition in America, which is our elections?" Buttigieg asked.

He also mentioned the statement by Federal Elections Commission Chairwoman Ellen Weintraub on Thursday reminding the public that accepting assistance from a foreign power is a crime.

"Let me make something 100% clear to the American public and anyone running for public office: It is illegal for any person to solicit, accept, or receive anything of value from a foreign national in connection with a U.S. election," Weintraub said in her statement, expressing disbelief that she had raise this topic at all.

Buttigieg mentioned how Weintraub "felt shocked that she had to remind everybody of this."

"But if you think there's a foreign effort to tamper with an American election and you're an American who cares about America, you call the FBI," he said.