In electoral politics, it is usually the party that is out of power that promises that a victory will end the rule of an unpopular congressional majority or president.
The usual message coming from a minority party during a midterm election is that they should be elected to serve as a check on the president. The message of checks and balances has an inherent appeal to many voters, because the system of checks and balances between the three branches of government is baked into America’s national DNA.