I don't take issue with challenging election results and have never stated otherwise. In my view, Trump had the right to contest those results, as he had an obligation to his supporters. Let's examine some distinctions between the 2020 election and those you mentioned.
The first difference lies in distinguishing between contesting election results and questioning the legitimacy of an election.
While I did acknowledge that Trump lost in almost all of the over 60 cases he and his legal team brought to court, you can verify this information from numerous independent, reliable news agencies. In contrast to the 2000 election, where a recount was halted to comply with Congress's set timeframe for result certification, Trump opted for a different path. He not only urged his followers to follow suit but actively encouraged them to disrupt the certification process. Violence wasn't a concern; in his words, "It's going to be wild!" All the points raised in this post can be substantiated by reputable, independent news agencies both domestically (US) and internationally.
In 2000, the infamous "hanging chads" led to a legal showdown in Florida, with both parties deploying legal teams. The Democrats were outmaneuvered by Roger Stone and his Brooks Brothers Riot. Despite bringing knives to a gunfight, the Democrats' loss was unsurprising. Bush fought harder, Gore didn't, and Bush emerged victorious. The Supreme Court ultimately settled the matter. On December 13, 2000, just over a month after the election and before the Electoral College votes were certified, Al Gore formally conceded, stating, "for the sake of our unity as a people and the strength of our democracy, I offer my concession." In contrast, Trump has neither formally nor informally conceded to date and did not act in a manner promoting unity or strengthening democracy. In the January 6, 2000 session, twenty House members filed objections to Florida's electoral votes. Gore, presiding as President of the Senate, ruled these objections out of order, and the electoral votes of all 50 states were certified. Bush was sworn in on Inauguration Day, with Gore in attendance, marking a notable difference from the events of 2020.
In 2004 Kerry conceded his defeat to Bush on the day after the election. There were concerns about the process raised by both sides, but I don't see the point of bringing them up since they were raised by both sides, Kerry conceded, and obviously there were no issues as far as certifying the results of the Electoral College. Bush was again inaugurated and Kerry was there to witness it. Again, quite different than what happened in 2020. Here's a link on the controversies if you're skeptical that these aren't facts and instead the product of a vivid imagination or just interested:
2016. The Associated Press called Pennsylvania for Trump at 1:35AM EST, putting Trump at 267 electoral votes. By 2:01AM EST, they called both Maine and Nebraska's second congressional districts for Trump, putting him at 269 electoral votes, making it impossible for Clinton to reach 270. One minute after this, John Podesta told Hillary Clinton's victory party in New York the election was too close to call. At 2:29AM, the Associated Press called Wisconsin, and the election, for Trump, giving him 279 electoral votes. By 2:37AM, Clinton had called Trump to concede the election. On Wednesday morning at 2:30 a.m. Eastern Time (ET), it was reported that Trump had secured Wisconsin's 10 electoral votes, giving him a majority of the 538 electors in the Electoral College, enough to make him the president-elect of the United States, and Trump gave his victory speech at 2:50 a.m. Later that day, Clinton asked her supporters to accept the result and hoped that Trump would be "a successful president for all Americans."
There were controversies and concerns; like in 2004 coming from both sides. Jill Stein contested electoral votes in certain states, but she's Green, not Democrat, and as I mentioned, there's nothing wrong with contesting, but when you lose, you lose, and if you respect the democratic process you put on your big boy pants, admit defeat, and for the good of the country wish the winner success during their term. As in '00 and '04 elections you brought up, the '16 results were certified on the required dates. People took to the street in peaceful protest (as is their right as Americas) which were not called for by the loser Clinton. No actions were taken by Clinton to mobilize her supporters to deny the results, take over the Capitol Building, "fight like hell," and disrupt the certification process. The protests did not involve police officers being beaten by protestors and protestors did not search out elected officials inside (or outside of) the Capitol Building looking to hang them or otherwise bring violence.
There's nothing wrong with contesting results and using lawyers and the courts to fight as hard as you can for as long as you can right up until the moment where Congress fulfills their Constitutional duty to certify the results. But 2020 was the only year where that long tradition of respecting the democratic process and peaceful transition of power was not only ignored, but pissed on.
For the record, the last time I voted Democrat in a Presidential Election was Clinton in '92; more because I was tired of 12 years of Reagan/Bush than I was a fan of Clinton. I was so disappointed in the Clinton years that I didn't bother voting in '96 which was made easier since I was outside of the country in a remote location and didn't feel I had anyone to vote for anyway. In 2000 I voted Nader. Out of the country in '04 and '16 (were I also wasn't a fan of Hilary and didn't vote for her). I'm not a fan of Biden either. Obviously I'm not a registered Democrat. What I am is someone who respects the democratic process and who is against authoritarianism. I'm also someone who accepts the reality of a situation without feeling the need to make up stories or deny reality when things don't turn out the way I'd like them to. I remember what I was taught as a child playing sports and am either a gracious winner or accept graciously accept my defeat without whining about my loss. And since my residence is not even close to being a swing state I've never felt bad about not voting because unlike declaring a winner based on the popular vote, the Electoral College system makes it so that your vote doesn't really matter if you live in a solid red//blue state like Alabama, California, W. Virginia, Oregon, etc
As far as Milei, of course his opponents are going to smear him and work to ensure his defeat in the next election. It's called politics and it's how that game is played and has been played since politics has been around. Surely you don't get upset when Trump smears people and works to defeat them in the next election since part of Trump's whole schtick is to give people childish nicknames and smear them before the self-proclaimed Billionaire tries to sell common people red hats or flat out begs them to send him $. And his supporters love it when he does and repeatedly open their wallets to give their hard earned $ to the most successful businessman history has ever known - so successful he has to sell hats, bottled water, steaks, etc., and beg for $ . I can't understand why you'd be upset, take offence, or even bring it up as an issue if other politicians and their supporters use the same smear tactics that Trump uses? Maybe that lack of understanding explains why you believe the 2020 election was no different than 00/04/16? The Devil's in the details.