If you go back 50 years...through the elections of Carter, Clinton, Obama & Biden, you can't find a true liberal among them. Moronic right wing talking heads are playing revisionist history to call any of those people anything but centrists.
Nor can you find any from those who lost like Gore (who almost won), Mondale, Dukakis, Hillary Clinton, etc.
The most liberal candidate on the last 50 years was George McGovern who lost 49 states in 1972.
The country as a whole has gone further to the right since Watergate via right wing talk radio and Rupert Murdoch's newspapers and TV stations, but that does not turn centrists into left wing extremists no matter what the fuck they say on those radio and TV nonstop lying prime time opinion shows that pretend they're news shows.
Now in that environment since 1975-1980ish, how is Bernie Sanders going to run against the firmly entrenched right wing media machine that now includes social media and foreign actors?
There's one thing about the right you have to admire and that's they have learned how to play the long game. 49 years to politicize and throw out Roe. It was originally a bipartisan 7- 2 decision. The constant push downward of the top tax rate while the deficit rises and the wealth gap widens.
The rise of the Federalist Society in 1982. The Reagan administration fast tracking Rupert Murdoch's citizenship because non citizens weren't allowed to own more that 10% of a TV station. The right's hatred of objective newscasters like Cronkite, Huntley and Brinkley, Reasoner, etc. and the major (and only) TV networks during and after Watergate that they have since obviously fixed by creating right wing news narratives to support their goals. They spent decades putting in place the system for a jerk like Trump to actually use that media machine to win.
And through all that it's time for Bernie to rise to power?
Really?
He'd have to run and win in swing states, he'd have to turn a red state or 2 blue for a cycle, he'd have to make liberalism magically become centrist and he'd have to have to popularity of FDR in 1932.
Good Luck with all that. He's a fine senator though.