Despite the constant media portrayal of disarray, 2017 was a productive year for the first unified Republican government in a decade. Not only did we pass a once-in-a-generation tax reform, we repealed ObamaCare’s most onerous and unpopular provision, the individual mandate.

Democrats should be anxious about heading into midterm elections as Americans reap the benefits of tax reform and deregulation. If Republicans maintain our momentum, we can retain our majorities in the House and Senate. Yet I fear we may be giving Democrats...