In the case of a tie vote, the presidential contest is to be decided in the House of Representatives under a very odd system in which the House votes by state delegations. Under the 12th Amendment, a candidate must win a majority (at least 26) of the states.
Under the current partisan make-up of Congress, 26 House state delegations are controlled by the Republicans, 23 by Democrats, and one is tied. In a tied presidential election, it is likely, but not certain, that Republicans would retain a majority of the state congressional delegations. Thus, a tie appears to give the election to Trump.
But to make things more complicated, there is no certainty that all members of the House would vote their party affiliation, especially given the antipathy of some Republican members toward their own president. When we consider the likelihood that in the case of an Electoral College tie, Biden will win the popular vote by racking up big majorities in high population states such as New York and California, some members might feel duty-bound to cast their vote for the popular vote victor to avoid a crisis.
Now let’s complicate matters even further and imagine a shift of House delegations that leaves the House deadlocked at 25 votes for each candidate. Under the 12th Amendment to the Constitution, in the case of an Electoral College tie for the vice-presidency, the Senate chooses the vice president.