The biggest clue is that none of the Trump campaign’s post-election lawsuits allege mass voter fraud, and many don’t concern fraud at all. For example, in what may have been the most significant case, the campaign challenged Pennsylvania’s extended deadline for absentee ballots. They lost in district court, that loss was upheld on appeal in a circuit court led by conservative judges. And Biden won Pennsylvania before those late votes were counted, so even if Trump won the case (which he didn’t) or the Supreme Court stepped in to overrule lower courts (which they probably won’t) it wouldn’t change the outcome.
Trump has conducted his presidency as if he’s the producer and star of the world’s greatest reality show, and relied on friendly media to venerate him and demonize his opponents. That’s why the reelection campaign got so angry when Fox News called Arizona for Biden, with presidential son-in-law Jared Kushner asking Fox owner Rupert Murdoch to reverse it, and Trumpists attacking the head of Fox’s decision desk, Arnon Mishkin: It undermined the alternative reality they were trying to create. Even worse, it came from someone Team Trump expected to help sell the lie.