What Trump is doing by challenging the legitimacy of the election results is rather unprecedented. I tried to think about the past Presidential elections to figure out if his hinting at possibly not accepting them matches anything that has happened in the past.
1800 - the problem in this election actually led to an Amendment to the Constitution. Jefferson beat Adams, that was not in issue. What was in issue was that Jefferson tied his supposed VP Aaron Burr in the electoral college and the Constitution gave the seat of the VP to the person that came in second in the EC. Burr didn't equivocally back down and it created chaos in the government. For a time. The federalists had to help get Jefferson the vote in the House to give him the Presidency and in doing so Alexander Hamilton began what turned into the duel, and his death, at the hands of Aaron Burr.
So Trump hinting he would not accept the results would make him Burr here. The Congress got the right thing done, and Burr killed the former Secretary of the Treasury and founding father, ended up being a traitor, and is remember in history as nothing more than the example of the very kind of power hungry aristocrats the founders were trying to protect the country from.
1824 - Andrew Jackson accused his political enemies of a corrupt bargain in the victory of John Quincy Adams. Jackson won the popular vote and the most college votes with Quincy Adams coming in second, but neither had a majority. Henry Clay came in third. And after weeks of backroom deals and trying to figure out how to solve the problem, Speaker of the House Clay led the House to give the election to Adams, and then Clay was appointed Secretary of State. Jackson and the Democrats were furious but Adams was sworn in and they spent the next four years fighting him tooth and nail and then obliterating him in the next election.
So Trump hinting he would not accept the results would make him Jackson here. Except Jackson did accept the results though he made it clear that it was political gamesmanship and then built a new Democratic Party that stood in its basic form until after the Civil War and into the 1960's. Trump is no Jackson, and if you want to say that Trump is going to rebuild the Republican Party after this election like Jackson did the Democrats, you would be wrong. Jackson brought more people into the party, Trump is doing the opposite.
1876 - Hayes Tilden. Another one that went to the House. Instead of doing their job like they did in previous years they created a committee to decide the election and the committee selected Hayes. But at least we get close to Trump's problem here. Because the reason it went to the House was that while Tilden won the popular vote by a lot, he was one vote shy of the majority of the electoral college requirement. And the reason for that was that four states were disputing their own results and each party in those states was accusing each other of fraud in the election. So this might be the closest thing we have to what is going on now. Except that once it was figured out that nothing like this had happened before - fraud accusations stopping states from counting their ballots or certifying their results - the two party's worked together and came up with the idea for the commission inside the House. And then that commission chose. So while there were accusations all of the place, in the end, the party's worked together to figure out a resolution and then abided by that resolution.
So Trump hinting he would not accept the results would make him... the states of South Carolina, Oregon, Florida and/or Louisiana here as they were the states that alleged voter fraud within their state systems. But they never fought the ultimate result of the House.
1960 - Nixon Kennedy. The stories are replete with tales of the Chicago Democratic Party throwing ballot boxes into the river to ensure Kennedy won the state. His margin was small indeed but he did win. And Nixon, never seriously challenged the results - at least in public. The Republican Party was apoplectic about the results and the accusations of fraud. Current histories teach that Nixon decided that the country was better served by not fighting, but the party didn't follow that line. Three days after the election several republican agents and officials began trying to challenge the results, filing suits in several states to demand a recount, and some recounts did take place. In the end though it didn't matter and Kennedy was sworn in. In a really really close election.
So Trump hinting he would not accept the results would make him.... Republican Party Chairman and Senator, Thurston Morton, who led the recount charge. Who lost. And then ran the 1964 campaign for the GOP as well. But Morton also eventually resigned his power because of the deaths of Robert Kennedy and Martin Luther King and the fact that his party failed to address the issues of the country like he thought they should. He was trying to be a good servant after the '60 election by most accounts. So comparing Trump to him isn't fair. But at least this is close. A little. Ultimately, Kennedy didn't finish his term so the problems the GOP caused him didn't really matter in the end, but the social upheaval of 1960 has lasting marks on the country.
2000 - Bush Gore. This went ultimately to the Supreme Court with accusations of every kind made against everyone who dared offer an opinion on the election from any side. Bush was tainted with the results but other factors ultimately led the country to focus their attention elsewhere. And after the recounts, and the Supreme Court and everything else that happened, Al Gore gave one of the most moving political speeches by a "loser" that you can give in that capacity. And accepted the results. And Bush was sworn in.
So Trump hinting he would not accept the results would make him..... no one. Because Al Gore had more class than Trump seems to have at the moment. Although you do have to grant that Gore led the effort for the recounts. In what was another extremely close election.
And all brings this back to Trump now - because by all accounts right now, this is not going to be an extremely close election. We should grant, for mental gymnastics alone, that if this election is very close - on the Bush Gore, or Kennedy Nixon, or Tilden Hayes scale, that sure, Trump calling for recounts and the GOP accusing the DNC of voter fraud, and mass hysteria by the political class is all warranted and pretty expected. But if it's not close? If Clinton gets to 300, 340, 360 or more electoral votes? What in the hell is he challenging? Voter fraud on the scale necessary to even come to that would be something that no political system outside of Iraq and North Korea could function with, and for all the outrage at the left in this country, there can't seriously be a member of this GOP who would, with a straight face, say that those elections are more fair than ours.
If this election ends up close, more power to Trump. Get every right wing lawyer in the country to file every injunction you can and let the system support itself and correct itself in the manner it was designed to do. But if you lose huge, which it looks like you are going to do? Then you better man up, stand in front of the cameras and make it very clear that the results are conceded. Because if you don't there is no precedent for that in our history. None. There is nothing close on this scale. And for someone running for President of this country to actually have the gonads to stand in front of 70 million people and say that he might not agree to the results? That is a person who doesn't deserve the honor of running for the office to begin with. And it is certainly someone that no one who has any respect for this country and its political institutions should vote for, support or even acknowledge. He may have been the very worst form of what a current GOPer looks like right now in this nation before. But now, he is a clear and present danger to the United States of America. And the people that would grant him the backing to give him the ability to make that statement as the current national leader of the GOP have no right to ever again call themselves a supporter of a party that gave us Abraham Lincoln, William McKinley, Dwight Eisenhower and Ronald Reagan.
I would say he should be ashamed of himself, but he clearly has no shame. Nor ability to understand what his ridiculous statement/non-statement means. This isn't a banana republic. This isn't 18th century France on her third republic in 14 years. This is a nation that has put in the hard work to make a republic that spans more acreage than any republic ever has, controlling more people than any republic ever has, influencing the world with more power than any republic ever has and it is a nation that requires adults in positions of power. We deserve to proud of this nation, even with all of its faults and failures, for what it has managed to do - exist for this long allowing the civilian transfer of ultimate power every 2 or 4 years without issue save one in 1861 when our greatest leader held it all together with his will, determination and life. Our right to vote in this nation is a calling to that form of leadership, not this. This is disgusting. And I am ashamed that I ever supported this party. And everyone that is member now should be to. His nomination should be rescinded immediately. Let Clinton win every state by default. That is the price we should pay for this. The GOP is dead to me.