Key Republican Senators are cautioning President Trump about his potential willingness to meet with North Korean leader Kim Jong Un.

Such a meeting could "legitimatize a person who is one of the really bad actors in the world," Senator John McCain, R-Arizona, told reporters on Monday.

The issue arose after Mr. Trump expressed a willingness to meet with the North Korean dictator on Monday. "If it would be appropriate for me to meet with him, I would absolutely, I would be honored to do it," Mr. Trump said in an interview with Bloomberg News. He went onto emphasize that it had to be, "under the right circumstances."

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McCain, the chair of the Armed Services Committee, laid out those circumstances in his view: "I think the only time you would consider meeting with Kim Jong Un is to discuss the details of the North Korean commitment to dismantle their efforts at acquiring nuclear weapons and the means to deliver them."

When asked if Mr. Trump's comments were a wise diplomatic move, the veteran Senator answered "no."

Another national security hawk, Senator Lindsey Graham, R-South Carolina, expressed caution but signaled that he was "open minded" about the matter.

"I would caution about that simply because you empower anybody you meet," Graham told reporters, "but if [Mr. Trump] can find a way to stop North Korea from developing an ICBM with a nuclear weapon on top of it to hit America and that includes meeting him count me in."

The pair of Senators also expressed concerns about President Trump's earlier White House invitation to Filipino President Rodrigo Duterte. Duterte's war on drug users has been widely criticized by human rights groups for extrajudicial killings.

"I do not agree with that either because the president of the Philippines is obviously in violation of basic human rights," McCain said weighing in on the invite.

But Trump has been complimentary, noting Duterte's "very high approval rating" in the same Monday Bloomberg interview. The White House defended Mr. Trump's invitation to the Duterte, tying it in with the effort to reign in North Korea.

"I think it is an opportunity for us to work with countries in that region that can help play a role in diplomatically and economically isolating North Korea," White House spokesman Sean Spicer said on Monday.

"Not a big fan of this guy in the Philippines," Graham commented later that evening. "I don't know what you're going to tell him but if you tell him to knock off all the extrajudicial activity and undermining the rule of law it's probably worth it. Otherwise it's probably not."