It was only a month ago that Republicans seemed to post substantial gains on the generic congressional ballot. They had pulled five percentage points behind Democrats by some measures after a Monmouth poll showed Democrats up by just two. That led to a wave of articles declaring that the Republican tax plan and strong economic growth had revitalized the party’s fortunes.

In February, it was hard to know whether the Republican surge would last.

A little over a month later, Democrats have recovered. The most recent Monmouth poll, published on Wednesday, gave Democrats a nine-point lead. Over all, Democrats lead the most recent generic ballot polls by around nine points, about the same as their standing before the tax debate began.

There’s nothing new about a short-term swing in the polls that fails to cause a big change in a race. So far this year, just about every big shift in the generic ballot has proved short-lived. Highly sensitive, short-term estimates have misled much more often than they’ve presaged a lasting change.

Democrats have generally maintained a consistent lead of seven to nine points in a less sensitive, longer-term estimate of the generic congressional ballot. As a historical matter, the generic ballot tends to be stable over the longer term.

But the stability is perhaps more surprising in light of the events of the last six months. Since early July, the Republican health care bill has been defeated, revived and defeated again. The special counsel Robert Mueller has indicted more than 20 people. The Republicans have passed a sweeping tax cut. There was the violent far-right rally in Charlottesville, Va.; national anthem protests; the birth of the “Me Too” movement; as well as mass shootings in Las Vegas and Parkland, Fla. The government shut down. The stock market surged. ISIS was routed. Who knows how many times the president tweeted.