Threatening to withhold federal funds is a pretty popular way of implementing de facto national policies that the federal government isn't allowed to do directly (I think that's how we got 21 as the drinking age), and Feinstein talks about it like it's a sure thing it the states would comply to get the money.
But we have a decade of evidence, via the ACA Medicaid expansion, that GOP governors are more than willing to turn down federal dollars for ideological reasons. That's before we got to how Ducey, DeSantis, Kemp etc. have acted regarding the virus. It'd be an absolute cluster.