A Democratic Senate aide told CNN that "almost every question" from Democratic senators on the call "has been about testing," and said that the administration "has not given clear answers."

The source said that at one point, Sen. Angus King of Maine, an independent who caucuses with Democrats, said to Pence and everyone on the call, "I have never been so mad about a phone call in my life."

King called the administration's failure to develop a more widespread national testing regime a "dereliction of duty."

Access to testing has been uneven throughout the country amid the pandemic even with efforts to expand capacity -- and pressure is intensifying on the President and the administration to ensure adequate testing, which is widely viewed as a requirement to reopening the shuttered US economy.

Most states have imposed lockdowns in an effort to halt the spread of the devastating pandemic, but the President has been pressing for states to soon start opening back up.

Trump unveiled new guidelines on Thursday meant to help states loosen their social distancing restrictions, but in a retreat from his onetime claim of "absolute authority" to restart the economy, he told governors it was their decision on when and how to reopen.

Asked why he was frustrated, King told CNN, "The administration should not be off-loading the responsibility for testing onto the states."

"This is an area where national response and coordination is a necessity," King said. "The states don't have the DPA (Defense Production Act) or the other resources of the federal government to oversee and coordinate the testing infrastructure, and yet, adequate testing is the basis of safely reopening the economy."

Hours later, at the daily White House briefing on his administration's coronavirus response, Trump said the federal government will "be sending out 5.5 million testing swabs to the states." The swabs, he said, "can be done easily by the governors themselves. Mostly it's cotton. It's not a big deal, you can get cotton easily, but if they can't get it, we will take care of it."

When he was asked Friday in an interview with PBS why there hadn't been more of a federal push for testing, Pence said the administration "has no higher priority than continuing to dramatically expand testing" and that the focus would be on activating "unused testing capacity" in labs.

"We actually believe that we could double the amount of testing that's taking place every day if we simply brought online all of the testing capabilities in all the labs," the vice president said in the interview. "And that will continue to be our focus, even as the President is continuing to drive our team forward on identifying new forms of testing."

The White House's new guidelines for reopening, meant to speed Trump's goal of restarting the country, won't be mandatory. Many governors have already extended restrictions into May or banded into regional collectives that will determine their own reopening plans. But Trump wants to provide at least a framework for how places can reopen despite warnings from all corners that testing capacity for coronavirus is still too small.

Despite signaling to governors earlier this week that that they would decide when to reopen their states, however, Trump sent a series of tweets on Friday calling to "LIBERATE" Virginia, Minnesota and Michigan, three states with Democratic governors. Michigan and Minnesota have seen protests in recent days as people grow concerned about the economic fallout from the pandemic with protesters voicing opposition to stay-at-home orders.

Near the end of Pence's call with Senate Democrats, Virginia Sen. Tim Kaine pressed the vice president on Trump's tweets to "LIBERATE" those states, according to another Senate Democratic aide. Kaine, the aide said, "asked Pence why the President was trying to incite division in the midst of a global pandemic."

Pence did not answer the question, the aide said, but instead, "tried to deflect by talking about how they are working respectfully with governors, and Kaine jumped back in to say that those tweets are not at all respectful."

Senate Democratic leader Chuck Schumer, according to the aide, closed the call saying that all of the Senate Democrats agreed with what Kaine had just said.

King was the first to "lose it" in a measured way, a source on the call told CNN, who said King was then followed by Kaine. Both came at it from the perspective of two former governors, the source added.

Another person on the call also said it did not go well, adding that the administration has no new plan for testing.

Democratic Sen. Chris Van Hollen of Maryland told CNN in an interview that there was "a lot of frustration" on the call.

"There's a big gap between a lot of happy talk from the administration and the realities states are facing every day," he said, "There's just this huge gap ... happy talk doesn't do you any good. Happy talk doesn't get you another N95 mask," he added.

"The only way to understand what's happening out there is to create an accountability mechanism and have more transparency. We want the administration (to) essentially put on paper, or put on the internet, what they're actually doing so we can compare what they say they're doing to what we're hearing in our states and from our providers."

Sen. Brian Schatz, a Hawaii Democrat, told CNN that the administration's "new plan sounds like the old plan, which is to declare victory and engage in magical thinking to try to survive another 24-hour news cycle."

"But they have not actually assessed how many tests they need every day," Schatz continued. "Their new declarations about the availability of rapid testing technology and ramping up capacity are alarmingly similar to the announcements made last week, last month and the month before. They are nowhere."

The tense call also comes as congressional Republicans, the administration and Democrats remain in a stalemate over how to provide additional funding for a small business loan program, for which funding has now run dry . Democrats have pressed to include additional aid for states and hospitals as well as conditions on how the loan program funding is used, while Republicans have been arguing that a clean funding increase for the program is urgent and that other issues can be dealt with in subsequent legislative packages.

This story has been updated with comments by Vice President Mike Pence.