Happy Monday and welcome to Overnight Defense. I'm Rebecca Kheel, and here's your nightly guide to the latest developments at the Pentagon, on Capitol Hill and beyond. CLICK HERE to subscribe to the newsletter.

THE TOPLINE: The coronavirus pandemic is bringing changes to the Pentagon, as it has for nearly every aspect of American life at this point.

On Monday, the Pentagon said it's creating a "bubble" around Defense Secretary Mark Esper Mark EsperTop admiral: 'No condition' where US should conduct nuclear test 'at this time' Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Oldest living US World War II veteran turns 111 MORE and Deputy Defense Secretary David Norquist by keeping them separated.

"Starting today, the secretary and the deputy secretary are remaining physically separated," Pentagon spokesman Jonathan Hoffman said at a briefing.

"They and their staffs will only interact via teleconference," Hoffman added.

By the numbers: At the briefing, officials also provided an update on the number of coronavirus cases for Pentagon-connected people.

As of early Monday morning, there were 37 confirmed cases of COVID-19: 18 active-duty service members, three civil servants, 13 dependents and three contractors.

Earlier: Late Friday, the Pentagon announced that all domestic travel is off limits until May 11 for service members, civilian employees and their family members.

Commanders can make exceptions for "compelling cases where the travel is mission-essential, for humanitarian reasons, or warranted due to extreme hardship," the Pentagon said Friday night.

The Pentagon also announced Friday night that all unofficial visits to the Pentagon – to include personal guests and friends of DOD personnel and contractors – are "suspended" as of Monday, as are visits from international partners and visitors.

More exercise changes: U.S. Africa Command (Africom) announced on Monday that African Lion 2020 was canceled out of "an abundance of caution."

It added that the decision was made "based on international travel restrictions associated with the novel coronavirus (COVID-19) and to minimize the risk of exposure to U.S. and partner nation service members."

Africom had previously said African Lion, its largest exercise, would be scaled back.

U.S. European Command (Eucom) also announced Monday that its Defender-Europe 20 exercise is changing in "size and scope."

Movement of personnel and equipment to Europe stopped Friday, and several exercises that were linked to Defender-Europe "will not be conducted," Eucom said.

"There are many details still being worked and discussed with our allies and partners," Eucom added. "Changes are anticipated to the deployment timelines of soldiers currently in Europe, redeployment of U.S.-based equipment and the next Atlantic Resolve rotation."

Balancing act: Over the weekend, The Hill's Ellen Mitchell took a look at how the Pentagon is balancing its response to coronavirus with continued threats from global hotspots such as Iran and North Korea.

Among concerns lawmakers have raised is the availability of coronavirus tests for troops in war zones such as Afghanistan.

At its Monday briefing, the Pentagon pushed back on reports that troops in Afghanistan don't have access to testing.

Tests are readily available, but the machine to process them is not in Afghanistan, the senior health officials for the Joint Chiefs of Staff said. Therefore, the tests must be shipped to the nearest military lab in Germany.

"I'm not aware of any lack of tests. I believe there's been some concern about the fact that the equipment to run the tests, that specific machine, is not in Afghanistan and that's true," Joint Staff Surgeon Air Force Brig. Gen. Paul Friedrichs told reporters at the Pentagon.

"What we do with any lab that we can't perform in a deployed environment is we fly it or ship it to the nearest lab that can perform it," he said. "That doesn't mean that they're not getting tested, we're doing the swabs, we're just not running the test itself in Afghanistan."

Beyond the Pentagon: President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE on Monday urged Americans to avoid traveling and gathering in public spaces in an effort to blunt the spread of the coronavirus, saying the outbreak could last into July or August.

"If everyone makes this change, or these critical changes and sacrifices now, we will rally together as one nation and we will defeat the virus," Trump said in the White House briefing room. "We're going to have a big celebration all together."

Trump announced the new guidelines during a press briefing Monday afternoon. Officials also recommend that Americans avoid gatherings of more than 10 people; avoid discretionary travel; avoid eating in bars, restaurants and food courts; and engage in schooling from home when possible.

"We'd much rather be ahead of the curve than behind it," Trump said.

The president's comments on Monday marked his most direct appeal yet for Americans to take the virus seriously and avoid public settings where the coronavirus can be easily spread.

Biden calls for mobilizing military: Former Vice President Joe Biden Joe BidenSenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE said Sunday he would mobilize the military to respond to the coronavirus outbreak, calling it a "national emergency" that requires the U.S. to react as if it is a time of war.

"I would call out the military now," Biden said at the Democratic presidential debate in Washington, D.C. "They have the ability to provide this surge that hospitals need. ... They have the capacity to build 500 hospital beds and tents that are completely safe and secure. It's a national emergency, and I would call out the military."

"We're at war with the virus," Biden added.

Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (I-Vt.) said he would mobilize the National Guard, as New York has done, to address the health crisis.

"We use all of the tools that make sense," Sanders said. "And using the National Guard ... that has to be done."

MEANWHILE ... IN IRAQ: The situation in Iraq remains tense after last week's tit-for-tat between the United States and an Iran-backed militia.

Over the weekend, the U.S. military said there was another rocket attack at Camp Taji that injured three U.S. troops and two Iraqi troops.

The attack happened at the same base where two U.S. troops were killed in a rocket strike Wednesday, leading to U.S. airstrikes on five Kataib Hezbollah weapons storage facilities in Iraq.

Pompeo's warning: Secretary of State Mike Pompeo Michael (Mike) Richard PompeoHouse panel halts contempt proceedings against Pompeo after documents turned over Outgoing ambassador to China slams Beijing over coronavirus: 'Could have been contained in Wuhan' Hillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers MORE told the Iraqi prime minister that the U.S. is prepared to act in self-defense if attacked in Iraq, according to a readout of a call between the two officials released on Monday.

Pompeo spoke with Iraq's Prime Minister Adil Abd al-Mahdi on Sunday and called on the Iraqi government to fulfill its obligations protecting coalition troops working in the country to defeat ISIS and identify and hold accountable the groups responsible for a rocket attack last week that injured three U.S. service members.

"These actions will not be tolerated and the groups responsible must be held accountable by the Government of Iraq," Pompeo wrote on Twitter.

US leaving smaller bases: The U.S.-led coalition in Iraq is leaving some smaller military bases in the country, the coalition said Monday, with most troops redeploying to elsewhere in Iraq.

Despite the timing of the announcement, the coalition framed the move as a result of the Iraqi military's successes, not the recent rocket attacks.

"As a result of the success of Iraqi Security Forces in their fight against ISIS, the coalition is re-positioning troops from a few smaller bases. These bases remain under Iraqi control and we will continue our advising partnership for the permanent defeat of Daesh from other Iraqi military bases," the coalition said.

NBC News, which first reported the changes, said the affected bases include joint bases at al-Qaim near the Syrian border, Qayyarah Airfield West near Mosul and possibly K-1 Air Base in Kirkuk.

ICYMI

-- The Hill: Senate clears 77-day extension of surveillance powers

-- The Hill: Military sees surge in sites with 'forever chemical' contamination

-- The Hill: Record percentage of Americans says defense spending 'about right': Gallup

-- The Hill: First US sailor on ship diagnosed with virus

-- The Hill: Pompeo warns China against spreading 'outlandish rumors' about coronavirus

-- The Hill: Trump, G-7 leaders agree to cooperate on coronavirus response

-- The Hill: VA confirms first death from virus

-- The Hill: Opinion: NATO's budget virus: How the pandemic could slash military spending

-- Bloomberg: F-35's $17 billion diagnostic system rife with flaws, GAO says

-- Stars and Stripes: US, South Korea seek to break cost-sharing deadlock with furlough imminent

-- New York Times: Once-accused al Qaeda sympathizer goes home