In the final Iowa poll to be released ahead of Monday's caucuses, J. Ann Selzer and the Des Moines Register are showing that Donald Trump still has a commanding lead, but that the race is still fluid in several other ways.

The two biggest news items from the poll are former president Donald Trump sliding below 50 percent - though still with a 28-point lead - and former UN Ambassador Nikki Haley sliding past Florida Governor Ron DeSantis into second place.

Haley's lead over DeSantis (20-16) is just outside the poll's margin of error, which is at +/- 3/7 percent.

The DeSantis campaign has gone through all 99 counties of Iowa, touring and meeting voters all over the state. But the overall dynamics of the primary have shifted away from him after a rocky start and a struggle to maintain momentum. Haley, meanwhile, rose from near the bottom of the pack to the second place spot after a series of good debates, though the recent CNN debate likely did not do her campaign any favors.

But while the poll's topline numbers are good for Haley, when you dig into the data, her prospects of getting any higher seem bleak.

Her unfavorability has jumped, and her supporter enthusiasm has remained low. What's more, NBC News' Kornacki explains in a later tweet, "Half of Haley’s voters self-ID as independents or Dems, and 77% of them have an unfavorable view of Trump."

Trump Remains the Favorite

The former president's current numbers make it appear he's on his way to re-nomination. Forty-eight percent "breaks George W. Bush’s record in 2000 of 43% for the highest support level in any final pre-GOP caucus DMR poll," Kornacki explained. "His lead of 28 points also breaks Bush’s record of 23."

But the non-Trump vote now outnumbers the Trump vote, meaning that voters in Iowa have been wavering. Trump's diehard supporters are fiercely loyal, but some analysts have suggested that his high numbers in the polling might be due to an inevitability perception. If, however, Trump is vulnerable - or should somehow manage to lose on Monday - you could see a lot of those potential voters look for a new candidate. 

Most likely, they'll transfer over to DeSantis, who is the closest in how he wields political power and rhetoric, though his focus on who and when to fight is narrower than the former president's.

Haley's best chances come from lingering, undecided moderate Republicans who have yet to find a place to call home. Chris Christie's withdrawal from the race likely had some impact on Haley's numbers, giving the most staunch anti-Trump voters a place to go.

Mother Nature vs. Caucus-Goers

The severe winter weather may just have an impact on all this, however. Behind the scenes, some have suggested blizzards and intense cold benefit non-Trump candidates - older voters support Trump in much higher numbers than other candidates, and one of the prevailing thoughts behind the scenes is that they are most likely to stay home in extreme weather conditions.

Still, if these latest poll numbers are anything to go by, an incredible number of Trump voters would have to stay home and DeSantis/Haley voters be near 100-percent motivation to show up in order to take Trump out.

Any weakness on Trump's part, however, may just convince voters to shift their allegiances, and that could be enough for Haley, who has a very clear path in New Hampshire if everything plays out exactly her way.

The Unknowns

One thing we still don't know is what candidates' internal polling shows. Typically, some campaign or other would have dropped an internal poll to help shape the media narrative, but all campaigns have kept their polling secret. This may suggest that internal polling is lining up with public polling. But it could also mean that campaigns are holding their fire, as it's still early on in the primary process.

The other thing that remains a mystery is how all this shakes out with the frontrunner facing indictments for well over a hundred charges in multiple states. If Trump were to be found guilty, or even in prison, that will almost certainly have an effect on the race.

But, with the way things have shaken out so far, what that effect might be is a mystery.