@craig10x
Big news during the financial crisis whan a MM fund went under $1/share. The fed government imposed more stringent rules after that, but its may still be possible, although very unlikely.

Only Vanguard Brokerage, has SIPC coverage: “Securities in your brokerage account are held in custody by Vanguard Brokerage Services, a division of Vanguard Marketing Corporation. Vanguard Marketing Corporation is a member of the Securities Investor Protection Corporation (SIPC), which protects securities customers of its members up to $500,000 (including $250,000 for claims for cash). Explanatory brochure available upon request or at sipc.org.” The available MM fund in that is their Federal MM which has a slightly lower interest rate, but earnings from it are not subject to state tax.

Also, SIPC does not protect against the decline in value of your securities.

Vanguard Prime MM is liquid in that you can move money in and out easily. electronic transfer to or from a bank account or write checks on it (minimum $250 per check)