Single-party control of Congress isn't unusual. Since the Confederate states rejoined the federal government after the Civil War, one party or the other has controlled the House and Senate by itself for three out of four Congresses. (In the early days it was mostly Republican control, but the 20th century was dominated by Democrats.)
On Monday, we looked at existing projections for how many seats the Republicans might pick up in the House and the Senate with the goal of figuring out how strong the party's grip on Congress would be, from a historical perspective. One metric to gauge this is how many seats the party has in either chamber. Another, the one we chose, was the percentage of the majority in the House and Senate. After all, a century ago, the Senate only had 96 seats, making an eight-senator majority slightly more powerful than it would be today.
Now that we can see how the Republicans did at a minimum and, with a few seats still to be determined, how well they could wind up doing, we can erase the uncertainty from our first post. This will be the most dominant Republican Congress since 1929, with an almost-certain 8 percent majority in the Senate and an 11.7 to 17.7 percent majority in the House. That trumps the party's 6.3/13.3 percent majorities in the 80th Congress that began in 1947. (Even if the party loses the Senate races in Louisiana or Alaska, it only needs two of the contested House races that remain to go its way to beat 1947.)
Two important notes. The first is that the Democrats have had more dominant single-party Congresses in the interim, by far. And the second is that only four years after the strong 1929 Republican Congress came to the Hill, it had been replaced by a much-stronger Democratic one, washing ashore in the wave that Franklin D. Roosevelt created.
It's unlikely that the Republicans will lose control of Congress by 2018, of course. It took the Democrats that took over the Congress in 2008 a full six years to hand it back to their opponents.