Now hold on here, Most of this is just false. The 2000 election that ushered in W. Bush's first time was, to be quite honest, rigged. Florida vote counts were immensely suspect, and the immensely conservative-aligned supreme court of mostly Reagan appointees handed the presidency to Dubya.
His reelection came because America was in the middle of its insane fascist humiliation spiral as a result of 9/11 (which was the result of increasing radicalization and anti-American sentiment due to the decidedly very not-leftist US government treating the middle east as its playground), during which being perceived as anti-war was considered tantamount to treason.
The failure of Garland's appointment was messier, but there was a path forward, simply taking the refusal to call a vote as tacit approval, something called "Inferred Consent" by Harvard Law professor Matthew Stephenson, and which Barack Obama, a literal Harvard Law alumnus and constitutional law professor at the University of Chicago would have at least been aware of as a concept. Note that this is not a path that was precluded by "leftists" but rather by Barack Obama's own insipid "they go low, we go high" mantra.
The Democrats and the capitalist media corporations were the ones to help MAGA cross the finish line: The Democrats elevated the Trump campaign as part of their "pied piper" strategy, and large media companies gave Donald Trump massive amounts of attention and airtime because he brought ratings (almost like they have an incentive under capitalist economic systems to promote fascists or something).
Anyway I want to cut straight to the last part about Gaza because it's the most interesting and revealing part of this thread. It's genuinely fascinating to me that so many liberals seems to sincerely believe (or want to believe) that people on the left "pretend" to care about an ongoing colonial genocide. It kinda betrays how hollow and empty modern liberal politics has become. Anyone who cares about an inconvenient issue must be "faking it" because the only alternative is that they sincerely care about an issue, and if they sincerely care, then that must mean they have a reason to care. No, it's much more cognitively frictionless to assume that people you dislike are as cynical and valueless as you are, and only adopt positions to hurt you and you specifically. Exact same logic as the MAGA obsession with "Soros-funded protestors" but in a blue tie.
Liberals are less mad that they lost, and more mad that they were asked to compromise with the left instead of simply being able to coerce the left into compromising with them. If they were actually mad that they lost then they would first be mad at Kamala Harris for running a shit campaign trying to reach out to non-existent "moderate conservatives" with fucking Liz Cheney, then they would be mad at Joe Biden for not dropping out until the last minute which compounded and magnified the strategic problems of the Harris campaign, then they would be mad at the Democratic party for continuing to insist on simultaneously maintaining a garbage neoliberal domestic policy focused on killing as many poor people as possible, while also declaring their fervent love and adoration for a genocidal settler-colony, and then they would be mad at the corporate donor class that drives the Democratic party to reject progressive change and move right at every opportunity. Instead, they get mad at leftists, first and last.
If the leftists had the power to shift an election purely on their own, and the Democrats ignored their demands, then that means that the Democrats were being bad at politics. If you think that leftists "cost" Democrats the election, then you should be angry at Democrats for failing to adjust their strategy to account for them. If you're not mad at them, then you'd have to concede that you don't actually think that the left-wing bloc is sufficiently important to listen to, and if they're not important enough to listen to then you'd have to concede that they can't carry the blame.