Rudy Giuliani.

I don’t mean to dunk on the guy unnecessarily, but the starting and finishing points of discussions about the reliability of early presidential primary polling comes down to those six syllables: Rudy Giuliani.

Before Giuliani was President Trump’s legal counsel, he was the former mayor of New York City, a guy whose New Yawky accent and overlap with a period of plunging crime in the city positioned him to emerge as “America’s Mayor” in the aftermath of the Sept. 11, 2001, attacks in Lower Manhattan. It was a lucrative political position, but Giuliani had the misfortune of leaving City Hall at the beginning of a two-term Republican presidency. By the time 2008 rolled around, Giuliani was ready to take the plunge.

A Gallup poll in December 2006, shortly after the midterm elections that year, offered good news for Giuliani: He was tied with Sen. John McCain of Arizona in the Republican field. McCain would seem to be the heir apparent, after giving George W. Bush a run for his money in 2000. But here it was, 2006, and Giuliani was where he wanted to be.

It all fell apart, thanks in part to Giuliani’s poorly chosen strategy of sitting out early contests until Florida. He went from first place in late 2006 to eighth place overall in primary voting once the election was over. The nominee was indeed McCain, for what good it did him.

But that’s the flip side to this coin. Yes, Giuliani was favored early and flamed out, but McCain was in a good position in early polls, too — and won.

Because there are already 2020 polls trickling out, we figured it was worth a review of polls from shortly after the midterms that preceded the past four presidential elections to give a sense of how much stock should be put into them.

The 2004 primary featured another Giuliani-type run: Sen. Joe Lieberman of Connecticut, who had been the Democratic vice-presidential candidate four years previously. A Gallup-CNN-USA Today poll in late 2002 had Lieberman ahead of the pack, but he never got actual traction in the primaries. Instead, the eventual nominee was Sen. John Kerry of Massachusetts, who polled just behind Lieberman in that early poll.

The second- and third-place candidates (as measured by primary votes) were candidates who’d been sixth and seventh in that first poll. This pattern recurs: the eventual winner at or near the top of the early poll and the runners-up emerging from lower on the list.

We see that in the Republican field in 2008, for example. With Giuliani cratering, former Massachusetts governor Mitt Romney and former Arkansas governor Mike Huckabee surged in primary voting. (Note that this isn’t delegate counts or caucus votes — just votes in the primaries.)

On the Democratic side in 2008, there was an upset, as you may recall. Sen. Barack Obama of Illinois was well behind Hillary Clinton in early primary polling but surged to pass her in the delegate count — if not the primary vote.

In January 2011, The Washington Post and our partners at ABC News conducted a poll of the Republican field. At the top? Huckabee and former Alaska governor Sarah Palin — neither of whom ended up running. That’s another problem with polling this early: It’s hard to know who’s actually running. (Foreshadowing.)

So Romney, in third behind those two, ended up winning. Former House speaker Newt Gingrich of Georgia moved from fifth to third. And coming from way back in the pack was former senator Rick Santorum of Pennsylvania, who ended up scooping up a ton of primary votes. Not enough, but more than that early poll might have suggested.

Which brings us to 2016.

First, there was Clinton. She had a big lead in polling at the end of 2014 and held the lead consistently for the whole primary. As you may recall, though, the race was a bit more complicated than that would suggest.

On the Republican side, the Post-ABC poll had former Florida governor Jeb Bush, House Speaker Paul D. Ryan (Wis.) and Sen. Rand Paul (Ky.) in the top three slots. Ryan didn’t run, and Bush and Paul got clobbered. (Bush finished in seventh.) Sen. Ted Cruz (Tex.) jumped from fourth to second; Ohio Gov. John Kasich hung around long enough to go from 13th to third.

But then there was Trump, who came out of nowhere to lock up the primary and, eventually, the presidency. Even if we had included him in that December 2014 poll, he probably wouldn’t have done very well. Who knew!

It’s hard not to notice that the eventual nominees in these six races came from the top three in polls taken two years in advance. But it’s also important to note that Trump emerged in front of a field that will probably look a lot like the 2020 Democratic field: crowded.

The leader in Democratic polling now could be a Giuliani. Or someone random in the middle of the pack could be a Trump. Buyer beware.