More likely streak of 3 winning elections for prez?

[Mister Mets]

Argument for Republicans: They have won one election and have a good chance of winning reelection. Democrats have taken some unpopular positions (late-term abortion, support for increases in immigration) and the primaries are structured in a way that incentivizes bad habits. It is entirely possible Pence will be able to run as an incumbent.

Argument for Democrats: Trump says stupid things. The Democratic frontrunner probably won'r run for reelection at 82, meaning they might have a new nominee at a time when the party will historically do well, and be positioned to run an incumbent when going for a third term, where they are historically disadvantaged.

[Mister Mets]

I went with the Republicans, since that requires two elections to go their way, rather than three for Democrats.

Even if the Republicans' chances of winning individual elections is a bit lower, this more than evens the odds.