It backfires IMO. The Senate fails to convict, and when rumors come out that Democrats want to try removing Reagan via the 25th Amendment, the public reacts negatively. Reagan's mental decline is pitied by swing voters, who fall for the line that the impeachment is just nasty partisan politics ahead of the election, while a lot of Republicans think there was nothing wrong at all with breaking the law to help the Contras. The drama does suck up a lot of airtime, however, so fewer Dukakis gaffes or Bush dog whistles. Liberals are also energized to vote.
Vice President George Bush (R-TX) / Senator Dan Quayle (R-IN) ✓
Governor Michael Dukakis (D-MA) / Senator Lloyd Bentsen (D-TX)