The largest downside is... not being able to secure a majority while ObaMao is in office - appointing new Alinskyites to SCOUS (Ginsburg born 1933, Kennedy born 1936, Breyer born 1938) and other key positions.
Replacing Mc-Conn-all with a Jr. Rat senator will (probably) correct itself after his/her seat is up for election in 6 yrs. In the mean time, ObaMao will reek havoc on the Rat party and that is waking up more people to the conservative perspective.
Right now, it's of utmost importance to protect border states from illegals voting, else red states will turn blue from the combination of blue-staters flocking out of failed statist utopias (CA, MI, NY, etc.), plus new ignorant immigrants able to vote themselves "free stuff" from OPM (Other People's Money). It's obviously a top priority from the ObaMao's new effort to buss large groups of illegals to various points across border states. Small states still have 2 senators each - which gives them an outsized influence in confirmations and foreign policy. Large states have electoral college dominance, which ensures presidential elections.
That's how the Rats continue to control the national agenda - executive branch and senate.
read the old book - “advise and Consent” and see how non-followers are treated. A most interesting read from the early ‘50’s and what’s happening today.
With republican control with Mitch at the head, do you think they would really oppose any communist that Obama put forward for SCOTUS?