It’s easy to focus on the fact that Tuesday’s Washington Post-ABC tracking poll shows Donald Trump at 46 percent and Hillary Clinton at 45 percent. While Trump’s lead isn’t statistically significant, it’s still a sign that a candidacy written off as recently as a few weeks ago is showing some signs of life.

But, the most interesting number in Tuesday’s poll – and the one that should worry Clinton’s campaign most – is the question concerning how enthusiastic people are to vote for the two candidates.

It’s a pretty drastic dip – and it coincides with the announcement Friday afternoon by FBI Director James Comey that new emails had been discovered considered pertinent to the investigation into Clinton’s private email server. On Thursday and Friday of last week, the Post-ABC tracking poll showed negligible differences in enthusiasm between supporters of Trump (53 percent said they were “very enthusiastic”) and those of Clinton (51 percent “very” enthusiastic.) But by our Tuesday morning track, enthusiasm among Clinton supporters had dipped all the way to 43 percent while Trump’s held steady at 53 percent.

That’s striking. And worrisome if you are a Democrat.

For all of the talk about the small percentage of people who remain undecided in this presidential election, the bases of each party are equally – if not more – important. Voting – even for base voters – is not necessarily a habit. Ask any politician what the hardest part of their job is and they will tell you that’s it’s ensuring the people who are for them turn out to vote.

Without an excited base, a candidate never gets to the point where swing voters matter. Given that, even a slight change in base voter enthusiasm can create major issues for a candidate. That goes double – or maybe even triple – in an election like this one where so many base voters are something short of thrilled with their party’s nominees.

We know that there are lots and lots of Democratic (and Republican) base voters who planned to hold their nose and vote for their nominee. But given any sort of excuse not to, they might just stay home. (Side note: Nothing – and certainly not the Comey announcement – would drive Democratic base voters to cast a ballot for Trump. But staying home hurts Clinton too.)

At the moment, it’s too early to conclude that Clinton’s current enthusiasm dip is anything more than a several-day blip. It’s totally possible that by the time voters vote next Tuesday, her enthusiasm numbers will be back at – or even above – the pre-Comey levels. But what we know now is that the Comey announcement coincided with a clear erosion in enthusiasm among Clinton backers. And that has to make any Democrat nervous this close to an election.

(c) 2016, The Washington Post · Chris Cillizza