The Constitution says that individual states' legislators can award their electoral votes to whomever they choose; it just takes an act of the state's legislature, in most states signed by the governor. It's never happened, but it is constitutional.
Meanwhile, election law and practical reality say that Trump can only continue to raise money from his donors if the election is still "live": so long as he doesn't concede.
Trump has strong reasons to push both: he's hundreds of millions of dollars in debt, and the day he leaves the presidency several states will probably begin prosecuting him for numerous crimes ranging from bank fraud to tax evasion to rape. I gave Trump $5 back in 2015 to get on his list (I do that with most presidential candidates) and am now averaging about a dozen fundraising pitches a day from the Trump campaign and groups that Donald Trump controls.
While they claim they're raising money for a recount and legal challenges, the fine print says that 60% of the money is going to an entity that Donald Trump controls, and authorizes him to repeatedly ding the credit cards of anybody dumb enough to contribute, well into the future.
In the last four years, the Trump operation has raised over $1 billion, and over $300 million of that has vanished, like with his Inaugural Fund, into various unknown corporations. It's entirely possible that all Trump's posturing right now is just a scam to keep that money flowing, to the tune of millions of dollars a day. And while Trump gets 60% of that money, the RNC gets the other 40%, money that can be used by Republican candidates like David Purdue and Kelly Loeffler in the upcoming Georgia runoff.
Both Purdue and Loeffler were trading on inside information during the Trump administration, making themselves millions, so it's entirely conceivable they're so corrupt they'd enthusiastically endorse such a fundraising scam even when most of the money goes to Trump.
While Trump and Senate Republicans would be the winners in this scheme, the losers include the very institution of democracy itself, which is currently under assault by anti-democratic autocrats from Brazil to Hungary, Russia, Saudi Arabia, China, Turkey and The Philippines.
Meanwhile the billionaires who control multiple states' Republican legislatures' are worried that Joe Biden will raise their taxes and restore protective regulations that keep them from profitably poisoning and polluting America.
If Trump's fundraising scam can raise enough doubt about the integrity of the election, these right wing billionaires could direct a few Republican-controlled state legislatures to give all their states' electoral votes to Trump, regardless of how the citizens of those states voted.
December 20 is the deadline generally used for states to certify a vote, although in 2000 it dragged on well past that. As long as Trump keeps running his fundraising scam, the pressure will be on captive state legislatures to change their electoral votes, or at least keep the possibility open.
In the meantime, faith in America's form of government is being shredded, doing deep and perhaps irreversible damage to America and democracy around the world. If there are any Republicans left who care about the future of democracy, now is the time for them to put an end to this madness.