Here's a thought experiment. Imagine that Hillary Clinton had won the 2016 election. Across the country we'd probably be seeing a renewed spirit of activism on the right — mass protests, the creation of new grassroots organizations, local Republican Party chapters overrun with volunteers, ordinary citizens getting involved for the first time — in what would amount to a Tea Party II. Analysts would be predicting a huge Republican wave in the 2018 midterm elections, enabling the GOP to solidify its stranglehold on Congress and statehouses. Publications would be filled with think pieces asking, "Will Clinton's election destroy the Democratic Party?"

How would you feel about that, compared to how you feel now?

It's hard to know for sure. Back in reality, though, progressive horror over the fact that Donald Trump is president of the United States is being tempered by thoughts of a wave election in 2018, and even more by the last few months' remarkable upsurge in left-wing activism. Marches for women, marches for science, thousands of local Indivisible chapters across the country, local Democratic Party organizations revived — a new movement that, as Michelle Goldberg points out, is largely being led and organized by women.

Conservatives look on that movement with a sense of unease, at the moment when they should be enjoying their control of both Congress and the executive branch. It seems that every change of power comes with an equal and opposite reaction.

It wasn't always this way. In the 1970s and 1980s, people believed that the GOP had a virtual lock on the White House, which they controlled for 20 of the 24 years between the 1968 and 1992 elections. At the same time, it seemed that Democrats would hold Congress pretty much forever, as they had done for all but a few years since FDR was president. But something changed in the 1990s.

First Bill Clinton got elected in 1992, and his election was immediately followed by a furious reaction from the right. Conservatives turned out in large numbers in 1994, enabling Republicans to take possession of both houses of Congress, which they would hold, with only one brief interruption, for the next 12 years. George W. Bush's election in 2000 led to the rise of the netroots, a new kind of liberal activism that bore its electoral fruit when Democrats took back Congress in 2006 in another wave election. Then Barack Obama was elected in 2008, giving rise to the angry and mobilized Tea Party. Which brings us to today, Donald Trump, and the flowering of activism he has produced on the left.

It seems like we're caught in an endless cycle, where every positive result (from whichever side you see things) is quickly followed by a powerful reaction from the other side, providing an impediment to whatever gains you thought you'd make. While it may provide relief at a particular moment, contemplating the seeming intractability of this cycle can be profoundly depressing. It may mean you'll never truly lose, but it also means you'll never truly win, no matter how right you might be.

Why did it start when it did? The most likely explanation is that the 1990s was when the political realignment that dates back to Lyndon Johnson began to reach its maturity. Before then, the Democratic Party was a sometimes-uneasy coalition that included liberal Northerners and conservative white Southerners whose antipathy toward the Republican Party was forged in the Civil War. Johnson's embrace of civil rights broke that coalition apart, sending Southern whites into the waiting arms of the GOP.

But it didn't happen overnight; it spooled out over the course of years, as the grip of old loyalties gradually gave way. By the 1990s, the GOP was dominated by a generation of arch-conservative Southerners who had begun their careers as Democrats — people like Trent Lott, Phil Gramm, and Jesse Helms. Bill Clinton would be the last Democratic presidential candidate to get significant numbers of Electoral College votes from the South.

The polarization we see today is in large part the end result of that realignment process. Both parties have become more ideologically homogeneous, which leads them away from the center on issues as individual members have more of an interest in serving the desires of their base than reaching across the aisle. On the right in particular, the rise of talk radio and Fox News in the 1990s created a hothouse environment in which both citizens and politicians were instructed on a daily basis that the other side was not just wrong but downright evil.

When you become convinced that the other party's president is a threat to everything you believe in and hope for — rightly or wrongly — once that person is elected, you're going to get mad. And anger is the best tool for political organizing there is. Particularly given the inevitable compromises of governing, it's infinitely easier to get thousands of people to go out in the streets to say, "This administration is a catastrophe!" than to get the same number to come out and say, "This administration is doing a pretty good job, all things considered!"

Does that mean we're doomed to remain in this endless cycle of reactionary politics, where anyone who wins only has a brief window to do anything before the other side comes storming back to obstruct things before they can swing the pendulum back, after which they'll be stymied by the reverse result, over and over in an infinite loop of miserable gridlock and retaliation?

I wish I could say I knew the answer. What all of us want, of course, is for the cycle to stop at the moment where our side is on top. Whichever side you're on, you probably won't be that lucky.