WASHINGTON — Sly maneuvering around third-party candidates is a time-honored, bipartisan tradition in politics.

Democrats and Republicans alike have long stealthily tried to help little-known names on the ballot who might siphon votes away from the opposing party’s nominees. The issue has suddenly become a top midterm storyline because of remarkable drama in Alaska, where Democrats carried out a gambit to place a second Dan Sullivan on the ballot, alongside a Republican senator with the same name.

But several other midterm battlegrounds also have outsider candidates who could swing a close race.

In Ohio, Republicans have spent more than $2.2 million to promote a socialist candidate in the state’s vital Senate race, aiming to pull votes from the Democratic nominee, former Sen.…