Sen. Joni Ernst (R-Iowa) on Sunday pushed back against President Donald Trump’s nonchalant response to North Korea’s recent missile strikes, calling for the U.S. to take a “strong stance” against the authoritarian regime.

National security adviser John Bolton said Saturday that North Korea violated United Nations Security Council resolutions by conducting several short-range missile tests.

But Trump, tweeting from Tokyo during his visit with Japanese Prime Minister Shinzo Abe, downplayed the missile tests and seized the opportunity to mock one of his 2020 Democratic presidential rivals, former Vice President Joe Biden.

“North Korea fired off some small weapons, which disturbed some of my people, and others, but not me,” the president tweeted. “I have confidence that Chairman Kim will keep his promise to me, & also smiled when he called Swampman Joe Biden a low IQ individual, & worse. Perhaps that’s sending me a signal?”

CNN’s Dana Bash on Sunday asked Ernst, a member of the Senate Armed Services Committee, whether she was disturbed by the airstrikes, which Bash noted were launched “right across the sea” from Japan.

“I find them very disturbing and certainly wouldn’t trust Kim Jong Un,” Ernst said on CNN’s “State of the Union.” “I think we need to keep our eyes on North Korea. I understand the president wants to maintain a relationship with North Korea so that we can work with them. However, those strikes are disturbing.”