If you can't see past the next election cycle lesser of two evilism will always appear the logical choice, and of course guarantee progressives are ignored ad infinitum.
The problem with the Gore/Bush election- and it took me a long time to realize this- wasn't down to too many people voting for Nader. Gore, a weak and uncharismatic candidate, actually won the popular vote; the problem turned out in retrospect that the number of people who voted for Nader, another weak and decidedly uncharismatic candidate, was too small to make any impression on the DNC/Third Way Republicans who actually call the shots within the Democratic Party. The message the controlling Republican wing of the Democratic Party heard was, "we obviously aren't Republican enough". Hence the flood of co-opted and recycled bad Republican policies that pass today as putatively Democratic.
The Democratic Party will continue on as the slightly less batshit crazy, slightly less evil twin of the Republican Party until the Third Way types are made to understand that they can be made vulnerable by choosing to be corrupted, cynical, unprincipled triangulators. And the price of course for this cynical strategy of triangulation is the inexorable continuing rightward shift of the center. The Democrats, thinking themselves tactically smart for winning elections, are losing the war to the strategic Republicans who get their policies enacted even if they lose elections. That is true eleventieth dimensional chess. The Republicans trade the Democrats the illusion of victory for the real thing.
Of course as long as the partisan blinders remain on it is impossible to see how you are getting gamed by a more clever opponent. The Democratic body politic, in spite of the polling showing progressive policies on a range of issues being popular with real majorities of the American public, have bought into the Republican/DNC/Third Way lie that Americans are a profoundly conservative electorate and enacting recycled bad Republican policy is the best we can aspire to. And of course the continual co-option of these wrong policies does in fact make them appear moderate and centrist lending them a respectability they have no business possessing.
As Democrats we like to think we are the cleverer ones and that the Republicans are a party of crazy zealots, religious whackos and uneducated hillbillies. And yes those groups exist within the GOP. Look at the dismissive ridicule we pour on them here. But our condescension blinds us to the fact that that same group of putative crazies is eating our lunch on a strategic level. We get our electoral victories; they steer the ship. And in case you haven't noticed the ship is yawing hard to starboard in spite of the fact that a majority of Americans when asked say they want it steered to port.