It is not cash, it is a tax payer liability

Kashkari Says Fed Has "Infinite" Amount Of Cash: "We Create It Electronically"

And as the central bank widens its scope, the retail bankers begin roilling up their sector. Fees go way up for the middle class, rate spreads become important and restrict consumer banking. The Fed is a tax agent, do not kid yourself. 

The Treasury is currently paying 2.5% = interest expense/debt (including social security).  That is a high tax when growth was predicted to be 2% or slightly below.

The only expected outcome is that the virus chasers defeat this thing, mostly, in one, maybe two quarters.  Anything else then the assumption the central bank can do anything is gone.

Best bet, educate the public, keep them out of emergency rooms, produce masks and gloves, and the virus hunters will at least drive thins thing to the level of a sever flu, and tests are showing this is possible. Like this, from WebMD::

March 18, 2020 -- The flu drug favipiravir is "clearly effective" in treating coronavirus patients, Chinese researchers say.
Their trial of favipiravir included 340 coronavirus patients patients in China. Those who received the drug recovered quicker and showed greater lungimprovement than those who didn't get the drug, the U.K.'s Daily Mail reported.
It's believed that favipiravir blocks the coronavirus from replicating in the body.

Kasshkari is doing the cheer leading, the expectation shaping. But at this point this is nutty, as is the stimulus.  Focus on one thing, refining social distance, wear masks and gloves, watch your temperature, stay home if sick or otherwise.  Trials are three days, shipping time across the globe; this is a very accurate, very responsive set of scientists.

Should the Fed buy munis?

I think that LA County is large enough to have its own Fed account, direct. So, I think the question is moot, government agencies need cash flow account management, including continuing access o money market funds. But then, that pre-supposes the small/large state divide problem is  reduced.  The Swamp has a sever congestion problem, has had onbe since the founding, the small vs large state dispersion.

But, in this case, sure buy munis, buy some large corporate debt.