Congress might soon need to declare war on North Korea, a key Senate Democrat warned Saturday.

"I think all of us in the Senate need to be prepared to step up and take on our constitutional responsibility which may in some cases be to support military action," Sen. Chris Coons, a member of the Foreign Relations Committee, told CNN.

North Korea tested unsuccessfully an intercontinental ballistic missile on Friday, hours after Secretary of State Rex Tillerson chaired a United Nations Security Council meeting calling for a "painful" economic crackdown on the regime. That effort can't succeed without the cooperation of China, long an enabler of North Korea.

"North Korea disrespected the wishes of China & its highly respected President when it launched, though unsuccessfully, a missile today," Trump tweeted Friday. "Bad!"

Coons, who praised Trump for choosing 'diplomacy first" with China to curb North Korea's program, faulted him for the Twitter diplomacy. "This is no longer reality TV," the Delaware Democrat said. "The way to conduct diplomacy is not through Twitter but by leadership by the national security team at the Trump administration."

Still, Coons acknowledged that the United States might have to conduct a "first-strike" attack on North Korea.

"We're not there yet and I'm not going to address the hypothetical," he said when asked for a specific scenario. "But I do think we have to take seriously the prospect that Kim Jong Un has nuclear weapons, is developing ballistic missile capability that could reach beyond South Korea and Japan and hit American territory, and that he has publicly stated an intention to attack the United States."