Today’s civics pop quiz: What happens if 3 or more candidates run for President and none of them get a majority of the electoral votes?
No really, what happens? Surely our constitution covers this, right?
Of course it does! Say hello to this part of the 12th Amendment:
The person having the greatest Number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed; and if no person have such majority, then from the persons having the highest numbers not exceeding three on the list of those voted for as President, the House of Representatives shall choose immediately, by ballot, the President. But in choosing the President, the votes shall be taken by states, the representation from each state having one vote; a quorum for this purpose shall consist of a member or members from two-thirds of the states, and a majority of all the states shall be necessary to a choice.
See, it isn’t as though presidential candidates need to get the most electoral votes of all candidates to become president, they need a majority of the available votes. If no one candidate gets a majority the House of Representatives, currently controlled by the Republicans, gets to choose the next President of the United States among the 3 candidates who received the most votes (this write-up covers the nuances of that in much better detail). Interestingly, this last happened in 1824.
Pretty much any way you slice it, this makes any 3rd party candidate a disastrous scenario for Democrats this November.
For instance, if Sanders were to run as an independent he would peel off votes from Clinton making it unlikely either one of them will get the required majority, allowing the House to select Trump as President.
This means Democrats want Republicans to rally around Trump, not reject him. If, outside the Republican party, the Republicans put up a moderate 3rd-party candidate, that candidate could pull enough votes away from Clinton and Trump to prevent either of them getting a majority. Then the House steps in and selects this 3rd-party candidate as President.
This is why if Clinton gets the Democratic nomination we desperately need Bernie to not run as a 3rd party candidate and for us Bernie supporters to rally around Clinton in the general election rather than a 3rd party candidate.
This is also one of the reasons the US has the two-party system it does.