You can pack the Court via simple legislation by having Congress expand the number of justices (famously, there’s nothing in the Constitution that requires there to be nine) but any red-state Dem who voted for that would be public enemy number one back home. Electorally, it would be tantamount to a retirement announcement. They’d risk a backlash to be good soldiers for their party by voting to confirm a Democratic Court nominee, even if their constituents were grumpy about it, but voting to pack the Court to wrest the majority from Republicans would be an order of magnitude more transgressive than that. If Democrats are half-serious about this, they’ll need not just 50 votes but 50 votes from safe seats. That’s probably impossible.
With an even split and a floater all you have to do is remove one constitutionalist. RIP Justice Scalia