Congress faced an attack before from a concerted effort to spread a deadly infectious disease, but today’s adversary has produced a far different set of reactions, ranging from confusion to fear.

The combination of the lack of medical expertise and a political environment that is quite poisonous, metaphorically speaking, has left Congress in a state of suspended animation. Congressional leaders on Tuesday rejected calls for the House and Senate to leave town and adopt the “social distancing” that some experts suggest could stem the spread of the coronavirus.

“We are the captains of the ship. We are the last to leave,” House Speaker Nancy Pelosi (D-Calif.) told her caucus during a closed-door meeting Tuesday, according to Democrats in attendance.

Pelosi’s comments came after Rep. Jerrold Nadler (D-N.Y.) and others suggested that Congress should at least adjourn and allow lawmakers to work from their districts and, if necessary, vote electronically. Democrats said that Rep. Mikie Sherrill (D-N.J.), a Navy pilot, had already opposed abandoning the Capitol, using the captain of a ship reference.

On Monday Democratic aides acknowledged the week’s schedule was fluid, especially after up to six members of the House and Senate announced they were quarantining themselves after contact with someone at a conference who was later got diagnosed with the virus.

With three of the next six weeks already slated to be the congressional form of spring break, some rank-and-file lawmakers want to just conclude a few must-pass items later this week and leave town until late April.

“We just don’t know where we are, how serious this is going to be,” said Sen. Pat Roberts (R-Kan.), who said he appreciates daily updates sent to his office from Vice President Pence, who is coordinating the response. “There’s a group of senators who say we ought to shut down, for our employees’ standpoint.”

It’s dramatically different from the congressional response to anthrax attacks in October 2001, when letters sent to a pair of Democratic senators were laced with the bacteria that contained the deadly disease.

A few dozen were exposed to anthrax, including two postal workers who died, and thousands took antibiotics as a precaution. The Hart Senate Office Building — in which half the senators have their personal legislative offices — shuttered for more than three months at a cleanup cost of $27 million.

Yet the Senate continued its business without any lengthy break, pushing ahead with the national security agenda following the Sept. 11, 2001, terrorist attacks.

On Oct. 15, 2001, a Monday, a staffer to then-Majority Leader Thomas A. Daschle (D-S.D.) opened a letter in his Hart office, discovering a threatening note and the anthrax.

Shortly after 5:30 p.m. the same day, the Senate held a procedural vote on a government funding bill. Two days later, as health officials realized the anthrax had spread deep into the ventilation system, they ordered the Hart building shut indefinitely.

But 4 o’clock that afternoon, the Senate plowed ahead and approved, on a 95-to-3 vote, a bill to fund the Interior Department. That same day investigators uncovered traces of anthrax in a mail room in a House office that processed all congressional mail, prompting the GOP majority to adjourn the chamber for the rest of the week.

They were ridiculed for ending the week so quickly.

“WIMPS,” the New York Post declared in a mocking headline.

The next morning, the Senate voted, 96 to 1, to fund military construction projects. Early the next week, the Congress was back in session, going almost full-bore until a few days before Christmas to handle the large post-9/11 agenda.

Veteran lawmakers say the coronavirus has created more uncertainty than even those early days of the war in Afghanistan when the anthrax letters started arriving in the Capitol.

“It was an entirely different thing. There, we knew exactly what we had. Here, we don’t know what we have. What’s going to be decided, I don’t know,” Sen. Patrick J. Leahy (D-Vt.) said Monday.

Leahy was the second Democrat targeted with an anthrax letter back in 2001, but he had already put a hold on all his mail arriving at the Capitol because three other letters — sent to the National Enquirer and TV news personalities — had been uncovered before his and Daschle’s letters were received.

Now, more than 3,700 have died worldwide, including at least 22 Americans, from the flu-like virus. While no lawmaker or congressional aide has contracted coronavirus yet, the nationwide ranks continue to grow each day as more Americans get access to tests for the virus.

Sen. Ron Wyden (D-Ore.) told reporters Monday that he has allowed some staff to telework to avoid any health threats.

Others remain confused about what members of Congress should do during next week’s recess, with many constituent meetings now in limbo.

“What a lot of us are looking for — and still are not satisfied that we have — are clear institutional policies to ensure that we as members of Congress do not become a vector of transmission,” Rep. Tom Malinowski (D-N.J.) said after Tuesday’s caucus.

Still, one key difference between anthrax in 2001 and the coronavirus today is the national political mood.

In the fall of 2001, uncertainty dominated the Washington psyche. For months afterward, mail to the Capitol complex, along with the surrounding neighborhood, was redirected to a plant that zapped letters to make sure any potential chemical or biological agent was neutralized. Investigators could not determine who sent the letters, with initial probes focusing on overseas terrorists.

Yet, in the wake of 9/11, Congress had rallied together, even singing “God Bless America” in bipartisan fashion a few hours after the attacks on New York and Washington.

After the anthrax attacks closed the largest Senate office buildings, senators and staff shared space with other offices. Leahy recalled a few senators setting up in his hideaway office in the Capitol.

Today, coming amid the 2020 presidential campaign, Republicans are accusing Democrats of trying to pin the blame on President Trump. “We might want to stop trying to politicize the damn pandemic, not a good thing. We haven’t done that before,” Roberts said.

Other lawmakers just want the public to know that members of Congress face the same threat from the virus as other Americans.

“Everyone needs to know that no one is exempt from this,” Rep. Barbara Lee (D-Calif.) said.