One potential downside if Trump runs third party if he loses a brokered convention.

[Shoulders of Giants]

Most people think its a good thing for Democrats if Trump runs third party, because it will almost certainly split the Republican vote and guarantee a Democratic victory for the president. That is certainly true, but there is a downside that most don't think about. If Trump ran third party, it would probably make Republican voter turnout higher than usual as a whole. The wingnuts would turn up to vote for Trump. The moderates would turn up to vote for whoever their official nominee would be. However, both would probably vote for Republicans for the House, Senate, Governors, and local elections. We Democrats on the other hand would only have one candidate on the ballot to encourage turnout, while they have two. Trump running third party may be great for the presidency, but horrible for every single other race on the ballot. What does everyone think of this?

[SCantiGOP]

1. Hadn't thought of it

Afraid you might be right. If ( and it's a huge IF ) they can keep the nomination from Trump his racist followers would probably just boycott the election unless he had his name on the ballot.
Only upside would be if he tried to establish a party that would run teaparty types for other races, which would be a huge boost for Dems, especially in the red states.

[tblue37]

2. A furious Trump might advise his fans to not vote for the GOP downticket.

Furthermore, many of them could be so angry about being cheated by the GOP establishment that they refuse to vote at all for the GOP downticket, because they refuse to vote for anyone with an "R" by their name, even though they would never, ever vote for anyone with a "D" by their name.

[Shoulders of Giants]

3. I would hope that he would do that.

Obviously he can't personally insult every single Republican all the way down to city dogcatcher. Hopefully he would spend a lot of time insulting vulnerable Republican Senators though.

[tblue37]

6. Not individually, but he can say that the Republcan Party is the enemy and turn his voters against

them, no matter what office they are running for. I hope he is driven to do that.

[Trenzalore]

4. How many states have sore loser laws?

I know in many states if you lose your party's nomination in a primary you aren't allowed to run as an independent in the general election.

[Chan790]

5. Having never been challenged...

it's widely thought that "sore loser laws" will not withstand judicial scrutiny.

[tblue37]

7. From Wikipedia:

In United States politics, a sore-loser law is a law which states that the loser in a primary election cannot then run as an independent in the general election.[1] In most states, these laws do not apply to presidential candidates. Many states accomplish the same requirement by having simultaneous registration dates for the primary and the general election; in fact only the states of Connecticut, Iowa, New York and Vermont have neither a sore-loser law nor simultaneous registration deadlines.[2]

In Michigan, one of the few states where this law applies to presidential elections as well, Gary Johnson was three minutes late to withdraw from the 2012 Republican Primary and was therefore on the ballot. As a result, he was denied ballot access as a Libertarian.[3] The Libertarian Party stated that since petitioning in Michigan is by party, not by person, a Texas businessman who is also named Gary E. Johnson would stand in and run for president as a Libertarian in Michigan, but a U.S. District judge denied their motion.[4] Gary Johnson was certified as a write-in candidate and received 7,774 votes in Michigan in the general election that year.[5]

Here is a link to an article that shows how he could run 3rd party:
http://thefederalist.com/2016/02/18/trump-can-probably-run-a-third-party-campaign-but-he-shouldnt/

SNIP

Most states’ deadlines to submit those signatures fall in August or September, but deadlines start as early as May, when 80,000 signatures are due in Texas. This is another opportunity for a potential Trump lawsuit: state laws that apply to federal elections are always under greater constitutional scrutiny, especially a state law that could impact the larger nationwide interest in such a huge way.

It’s hard to predict what would happen if Trump were to challenge the early deadline states to push those deadlines back for him. Given his incredible polling numbers, compressed calendar, and seemingly bottomless funds, it’s hard to predict whether he’d struggle to meet those deadlines in the first place. He may not need the legal tantrum at all.

SNIP

[Trenzalore]

8. So basically Trump can run 3rd Party

Doesn't stop him from endorsing someone else though.