We are about to be deluged with polls on the Democratic presidential nomination race. Heavy drops of data have already started to fall.

But keep in mind one thing about polls: They change.

Between now and early 2020, the numbers will fluctuate, maybe frequently and dramatically. That doesn’t mean today’s top candidates will sink, or today’s bottom feeders will rise, but it does mean big shifts can occur abruptly.

Currently, former Vice President Joe Biden tops the polls. Despite a rough patch over the past few weeks, he’s still popular with 70 percent of Democrats.

Assuming he runs, Biden’s front-runner status will be questioned many more times in the months ahead. Can he take the punches? Will his age hurt? Will his mouth trip him up? If not Biden, then who? Can U.S. Sen. Bernie Sanders overcome his age and socialist label? If not Sanders, will South Bend Mayor Pete Buttigieg dazzle Democrats and sweep the convention as the unconventional candidate? Or will U.S. Sen. Kamala Harris become the compromise choice?

Voters view presidential elections through kaleidoscopes. At certain moments they focus, give it a turn — and then everything shifts. Examples are vivid, and plenty.

In April of 2015, former governors Jeb Bush and Mike Huckabee were leading the national polls for the Republican nomination, with Gov. Chris Christie, U.S. Sen. Rand Paul and U.S. Rep. Paul Ryan closely behind. Not long after, the kaleidoscope shifted. U.S. Sen. Marco Rubio started edging the field. Then, briefly, Gov. Scott Walker took his turn on top, as did physician Ben Carson.

As we know, these eight men ultimately didn’t cut it.

Enter Donald Trump. Early polls did not even include his name. The one poll that did peg his support at a meager 3 points. But after Trump entered the race in June of 2015, he zoomed to the top. Even though Carson displaced him a few times, Trump led the rest of the way, with U.S. Sen. Ted Cruz his most formidable opponent.

It wasn’t only the 2016 race that flipped back and forth. The 2012 campaign gave pundits whiplash.

At this point in 2011, Mitt Romney led the polls. In late summer, Gov. Rick Perry blasted him out of first place. Then, Romney came back after Perry stumbled, only to lose the lead to businessman Herman Cain in the fall. For most of November and December, former U.S. Rep. Newt Gingrich emerged as front-runner. He lost the baton in January when Romney popped back up, although the former Speaker of the House regained it briefly at the end of the month.

Continuing with these musical chairs, the next polling front-runner became former U.S. Sen. Rick Santorum, who grabbed the perch in February for about a month. Romney didn’t regain first-place until March, when primaries and caucuses were well underway.

Democrats have seen similar shifts. At various points during their 2004 nomination race, Gov. Howard Dean, U.S. Rep. Richard Gephardt and Gen. Wesley Clark were front-runners. That was before U.S. Sen. John Kerry nabbed the prize.

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Going into 2008, Hillary Clinton was the big favorite. Then Barack Obama jumped in. After the first slow months of his campaign, Obama gained steam. He and Clinton were to joust for first place until the last primary votes were counted.

These stories make a point: Candidate fortunes, especially in the early stages of a presidential nomination contest, can shift wildly.

Keep in mind that the polls we’re talking about are only pictures in time. They’re not crystal balls. As voters focus and refocus, numbers rise and fall. That doesn’t mean polls are wrong, it means events happen and minds change.

Here’s some advice as we prepare for the upcoming primaries: Don’t think the race will look the same in August or October or February as it does in April.

Remember, it’s about kaleidoscopes.

Ron Faucheux is a nonpartisan political analyst and author of Running for Office. He publishes LunchtimePolitics.com, a daily newsletter on polls, and lives in New Orleans.