With 17 days before the Iowa caucuses, the chattering class will hang on every poll and strain to hear every gaffe, trying to discern movement toward one candidate or another. A Reuters-Ipsos national poll shows Sen. Bernie Sanders (I-Vt.) moving into a tie with former vice president Joe Biden! But wait: Emerson’s New Hampshire poll shows Sanders’s lead falling (down by three points), with Sen. Amy Klobuchar (D-Minn.) coming on strong! Political-watchers should keep their eyes on several moving parts, while remembering that a single poll can be either an outlier or a leading indicator.

First, in a bizarre way, impeachment might wind up inuring to Biden’s benefit. With every eye-popping revelation — from the letter written by Trump lawyer Rudolph W. Giuliani to the notes from Giuliani’s associate Lev Parnas — one can sense the abject panic that apparently overtook President Trump over the prospect of facing Biden. Biden has already begun to make use of Trump’s obsession with him:

In Houston on Thursday night, Biden told donors at a fundraiser, “I’ve learned three things in the last couple months: Number one, Vladimir Putin does not want me to be president. ... Kim Jong Un of North Korea doesn’t want me to be president either. . . Thirdly, I know that Donald Trump doesn’t want me to be the nominee, and I wonder why.” Biden is banking that the crazier and more dangerous Trump becomes, the more voters will seek a familiar face to pick up the pieces.

Second, Sanders is caught up in an internecine fight with fellow progressive Sen. Elizabeth Warren (D-Mass.), and it is far from clear which, if either, will benefit. As Sanders moves to strengthen his socialist credentials, he risks scaring off Democratic voters worried about electability. How is this guy going to stand up to Trump? Have Democrats even vetted Sanders?

Joe Lockhart, a former spokesman for President Bill Clinton, raises precisely this fear, observing that “there has been far too little discussion of Sanders’s 50-year record, nor have we seen a real view of how he would defend that record against a Republican onslaught. ... The result is that one of the leading candidates for the nomination has largely escaped the kind of scrutiny his opponents have been put through and that should worry every Democrat.” (Lockhart fishes out just a few problematic nuggets from Sanders’s past, such as his call to abolish the CIA, his campaigning for the Socialist Party and his praise of left-wing dictators.) Now that Sanders has declared war on Warren, she and others may well return fire.

Third, the second choice of caucus-goers supporting candidates who do not make the 15 percent threshold becomes increasingly important in determining the order of finish. If Klobuchar does not make that benchmark, do her supporters go to Biden? To Warren? (After the flap about Sanders’s view of a woman’s ability to win, they might be less inclined to go for Sanders.)

Fourth, with all candidates claiming that they are the most electable, the conversation has shifted to turf more friendly to the candidates perceived as less “risky.” If the discussion is no longer about ideological purity, the candidates who voters think are more electable (Biden tops the list in most polling) figure to benefit.

Finally, we really do not know whether impeachment will rivet the country, sucking up all the oxygen. Will senators sitting in judgment of Trump suffer from their absence in Iowa or gain by their proximity to critical events?

In sum, the race has never been more fluid. The outcomes in Iowa and New Hampshire remain highly uncertain, and those contests’ impact on the race as a whole is equally unpredictable. After a year of campaigning and seven debates, the race is no more settled than it was when we had 24 candidates.

Read more by Jennifer Rubin: