Until recently, it looked like Republicans were almost certain to retain control of the U.S. Senate following the 2018 mid-term elections. Many commentators noted that Nancy Pelosi's team might have a shot at winning control of the House. But the Senate was different. Only a third of the Senators stand for election each cycle and the GOP was protected by a very favorable electoral map.
Only one GOP Senator (Nevada's Dean Heller) is running for re-election in a state won by Hillary Clinton. The only other soft spot in the GOP lineup is Arizona, where Senator Jeff Flake's fights with President Trump made it impossible for him to win re-election. Flake dropped out and there is an open seat in this toss-up state.
But, Republicans assured themselves, even if the Democrats win both Arizona and Nevada, they still end up only with a 50-50 tie in the Senate. In that case, Vice President Mike Pence would cast the tie-breaking vote to keep the GOP in charge.
All of a sudden, though, the landscape has shifted to give the Democrats a clear path to disrupt that narrative. The immediate cause of the shift is Alabama's Republican Senate candidate Roy Moore. It is virtually impossible for a Republican to lose a Senate seat in the South, but Moore's well on the way to proving it can be done.
If Democrat Doug Jones defeats Moore, the GOP majority will dwindle to 51-49. Picking up Arizona and Nevada in 2018 (while protecting all their own seats) would give the Democrats a Senate majority. That's not an unreasonable expectation given last week's election in Virginia.
However, the GOP problems are deeper than just Roy Moore. The underlying difficulty is their collective failure to deliver on campaign promises. After seven years of promising to repeal Obamacare if they had the power to do so, they didn't. Some Republican voters blame Donald Trump for not having a sound legislative strategy. Others blame Congressional Republicans for behaving the way Congressional Republicans always behave. Regardless, the bottom line is that voters did their part and their leaders did not. Some GOP voters may simply conclude it's not worth the effort.
Additionally, because there are always surprises in politics, other seats may open up for the Democrats. While sad to contemplate, there is a reasonable possibility that John McCain will leave the Senate early. If that happens, Arizona will become the third state in half a century to host two Senate elections in the same year. And, it's quite possible that Republicans could lose both.
To be clear, I am not saying that the Republicans will lose control of the Senate in 2018. The Democrats have problems of their own including a message that doesn't resonate in large segments of the country. And, they are defending ten Senate seats in states won by President Trump. The Republicans have legitimate pick-up opportunities in several of them.
At the same time, it's important to note the seismic shift in the midterm election dynamics. If the Democrats win in Alabama, they will for the first time have a clearly definable road to victory in the midterm Senate elections.