Sen. Angus King vented his frustrations about the Trump administration’s coronavirus response directly to Vice President Mike Pence on Friday during a conference call between the administration, calling the administration’s failure to rapidly expand testing a “dereliction of duty.”

“I have never been so mad about a phone call in my life,” King said during the call, multiple members of the Washington press corps reported on Twitter.

So far, President Trump has shifted much of the responsibility for responding to the deadly pandemic to state governors.

Phone call with Senate Ds and Pence was dominated by testing Qs and got testy, per source:

At one point, @SenAngusKing said “I have never been so mad about a phone call in my life” and said admin’s failure to develop an adequate nat’l testing regime is a “dereliction of duty.”

— Seung Min Kim (@seungminkim) April 17, 2020

Call with Pence and Democratic senators did not go well, according to one Democratic source: “It got to the point that Senator Angus King just said to Pence.. 'I have never been so mad about a phone call in my life.'"

— Lauren Fox (@FoxReports) April 17, 2020

“The States have to step up their TESTING!” Trump tweeted Friday about 12:30 p.m. It was unclear what time the phone call took place between the administration and the Senate Democrats.

King and 44 other senators signed a letter earlier this week addressed to Pence, calling on the Trump administration to conduct a comprehensive inventory of the nation’s supply of testing kits, chemical reagents and equipment. King and the group of senators also called for public disclosure of testing data and results, and urged the administration to release a detailed plan to address test shortages and gaps in the supply chain.

“Widespread diagnostic testing is crucial to controlling the COVID-19 outbreak,” the senators wrote in the letter. “In the long run, experts have argued that widespread testing will be needed to track and contain COVID-19 cases, allowing communities to slowly lift general social distancing restrictions without putting the public at risk.”

This story will be updated.