Let me be clear: I didn't support either Trump or Biden for the Presidency. And 4 years back I didn't support either Clinton or Trump. I didn't challenge Trump's victory in 2016 and I don't doubt Biden's victory now. (The remaining outstanding states were called late this week (e.g., CBS on Frday) with Trump retaining in North Carolina and Biden flipping Georgia. Some election desks haven't called Georgia because of a mandatory recount in process; note that recount reversals are extremely rare--like 3 of 27 statewide recounts over 15 years. The biggest swing was about 1250 votes for Gore in Florida 2000, not enough to reverse the election. Biden won Georgia by over 14000.)
Now I've never liked Trump's attempts to redefine voting or other constraints to suit his own purposes. Take his birther opposition to Obama. To be honest, I've never been a fan to the nativist specification for the Presidency, a Constitutional anachronism like the USPS. I have known naturalized citizens who are at least as committed to the US as any born Americans like me. I can remember a few years back that bodybuilder/actor immigrant Arnold Schwarzenegger was arguably the most popular politician (as newly elected California governor) in the US. There was some talk of a Constitutional amendment to enable his theoretical run for the Oval Office. But I remember thinking (long before Arnold's gubernatorial career ended with him deeply unpopular) why shouldn't the American people have the same option as California voters to put him into office? I remember there were nativists unhappy with the fact that John McCain, a military brat like me, was born in Panama. Similar things have been said about Ted Cruz and others. I have political differences with the late McCain, Cruz and others, but none of them involve the incidental facts of their births.
Recall that Trump was a registered Democrat who embraced Hillary Clinton and even Barack Obama in the 2008 election. I also knew he had Presidential ambitions by the 1980's and in fact briefly ran for the Reform Party nomination in the 2000 race. He, of course, wasn't the first to embrace nativism, but I was astounded how the same people who called Romney and others RINO's (Republican in Name Only) were strangely quiet over Trump's quixotic political odyssey. Trump was no principled conservative; he was pro-government. His only issue with Big Government is that he wasn't running it. It was obvious to me his only interest in the GOP was it seemed an easier path to the Presidency. He knew that the populist media conservatives like Rush Limbaugh had gone nuclear over "illegal immigration". I think he knowingly saw nativism as his bridge to the GOP base, and he decided the birther rubbish was his toehold into GOP politics. Being open-immigration, I was not just repelled by the fact of the rubbish behind the conspiracy theory, bur the mere implication that born Americans had to resort to technicalities versus the free market of political speech to make their case against Obama.
A similar concept is on the whole election setup. Trump for months has been railing against vote by mail schemes, over unspecified, unsupported allegations in the context of a global pandemic.
I never really doubted Obama's Hawaiian birth, but it seemed absurd that people were trying to get Obama disqualified from voter choices based on Constitutional sophistry, looking for a legal technicality. Make no mistake; I do think there are challenges to vote by mail (e.g., chain of custody, etc.) versus in-person balloting internal controls. I also thought the virus spread fears of polling places (vs., say, grocery stores) were wildly exaggerated. But elections have always been a state vs. federal government responsibility, and we always knew that there was going to be a lag between election returns and mail/absentee ballots postmarked by Election Day or drop box delivery. Trump opposed vote by mail every step of the way to the point that retirement of postal sorter equipment close to the election came under scrutiny and there were USPS warnings over prompt delivery of ballots. Yet he also opposed drop boxes. Why? Primarily Democrats have dominated early voting, and Republicans have relied on a strong Election Day turnout. Trump knew that a strong advantage he might hold say in MI and PA would likely be eroded as mailed ballot tabulations continued on the days that followed. (In some states, these couldn't even start until Election Day.)
Some Trumpkins tried to make an issue, say, of Pennsylvania state laws giving an 8 PM deadline for mail ballots to be received. The Pennsylvania Supreme Court in September basically allowed a small grace period to accommodate mail delays in receiving ballots postmarked by Election Day. (Similar policies often accommodate, say, military troops overseas.) Note that only a small number of (uncounted) ballots (about 10000) arrived during the grace period, and Biden's lead was unaffected by that amount.
That being said, I would have much preferred for Pennsylvania's legislature to accommodate the large labor-intensive vote by mail upgrade, to enable some earlier processing of email ballots, etc., instead of depending on the state court to make an accommodation. But once the court decision was made, voters made decisions on sending in ballots based on the rules as they understood them. Disenfranchising these voters for things beyond their control, like the timely delivery of their ballots, is fundamentally unjust and tyranny of the majority over individual rights. There is no moral justification for this; we are not even talking about the weeks after the infamous 2000 Florida election. It's another thing about accepting ballots physically cast after Election Day trying to manipulate election results.
As I write, Biden has 51% of the popular vote, almost 6 million more votes than Trump. Trump didn't flip a single Clinton state, while Biden flipped AZ, WI, MI, PA, and GA. Trump's abrasive personality may have scored with his base, but it was toxic with women voters in general. He had one of the highest unfavorable ratings in history; his first-term job approval ratings were at a historical low. He was never able to articulate a second-term agenda, and in an era where many, if not most governors have seen their ratings improve under the pandemic, his own handling of the crisis has gotten low marks across the board; in fact his own Administration has been a hotspot for COVID spread, including himself.
So we don't need a nefarious political plot to explain Trump's defeat. The midterms gave him a warning, and he didn't adjust. He has no one to blame but himself.