Sen. Angus King vented his frustrations about the Trump administration’s coronavirus response directly to Vice President Mike Pence during a tense conference call Friday, 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.

King’s “dereliction of duty” comment was described to The Washington Post by a person who joined the hourlong call but was unauthorized to discuss it and granted anonymity. Contacted Friday night, King spokesman Matthew Felling would neither confirm nor deny to the Press Herald whether the senator used those words because Felling did not listen to the call.

Later Friday, King publicly expressed his anger with the administration, which he says is offloading its responsibilities to states.

“If you know me, you know I’m a pretty even-tempered guy – but right now I’m angry,” King tweeted Friday evening. “We need widespread testing to understand the scope of this problem and the administration has the tools to lead the charge.”

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 between the administration and the Senate Democrats took place.

King and 44 other senators signed a letter 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.”

King was not available for an interview with the Press Herald on Friday evening, a spokesman said. But in a statement, King said the Trump administration is abdicating federal responsibility when a national response is a necessity.

“The problem is the president is now trying to offload onto the governors the responsibility for testing – and the governors aren’t in position to take that on. They can scramble around and compete amongst themselves for the materials – the chemicals, the vials, the machines, all those things – but they can’t really do it in any comprehensive way. That’s what the federal government can and should do,” King said in a statement to the Press Herald.

“The president has something called the Defense Production Act where he can say we are going to produce these numbers of machines and he can break down the bottlenecks. He has the CDC, the Department of Health and Human Services, Department of Homeland Security – he has a lot of tools to help us with this testing problem. To turn it over to the governors, as if they can magically make these things happen is an abdication of federal responsibility,” King said.

An unnamed Democratic aide told CBS News that King’s comments came after administration officials did not give clear answers to senators’ questions about coronavirus testing. Pence responded “politely,” but said he thought King was “misunderstanding a few things,” the source told CBS News.

After Pence’s response, Assistant Secretary for Health Greg Girior jumped in and said, “We were slow in the first few days,” but argued the administration then ramped up testing efforts, according to CBS News.

King also participated in a conference call on Thursday between Trump and senators from all parties. While King noted in an interview Thursday that the specifics of the call were confidential, the senator said that, generally, there was “a lot of ‘let’s reopen soon’ and ‘let’s do more testing’ ” from the president.

“I’m in the do more testing camp,” King told the Press Herald.

King described Trump as “non-confrontational and non-partisan” during the call, even complimenting Democrats for their work on the coronavirus emergency relief bills passed through Congress. But King said the president shouldn’t be suggesting, as he did again this week, that the responsibility for ramping up testing rests largely with governors.

King said the country needs a Manhattan Project-sized effort to expand testing capacity and called on the president to use his executive authority under the Defense Production Act to get manufacturers to help in that effort.

“Whether he will take to heart the advice of numerous senators who talked about the importance of testing, we will have to see,” King said Thursday.

Sen. Susan Collins was not among the 45 senators who signed the letter to Pence. Her office did not respond to an interview request Friday night.