The last four polls from the state had it McDaniel by four, Cochran by five, Cochran by one, McDaniel by two. Overall poll average: Dead heat. There is, in other words, a very real chance that tea partiers, having been thwarted in Kentucky by McConnell, are going to beat their third GOP incumbent in as many cycles after all tonight in Mississippi. Here’s your thread to follow the returns, which could run late given how close the race is. Everyone grasps the basic dynamics of the race — establishment versus tea party, pork-procurement versus ideology — but don’t overlook age as a factor in the outcome. This tidbit from FiveThirtyEight’s Harry Enten caught my eye:

Although it's only 4 polls, the correlation between % of 65+ makeup of MS-Senate voters in a poll & Cochran's lead is 0.99.

— (((Harry Enten))) (@ForecasterEnten) June 1, 2014

The more probable age turnout probably puts McDaniel up a point… but far too close to call…

— (((Harry Enten))) (@ForecasterEnten) June 1, 2014

If seniors turn out strong for Cochran, it may be enough. Age has actually played several roles in the race, not only as a proxy for Cochran’s endless tenure in D.C. but also, of course, as an element of his wife being harassed in her nursing home by that blogger. A few writers who’ve been covering it also couldn’t help notice that Cochran himself seems a step slower these days than he used to be. Dave Weigel calls it the issue that no one wants to talk about. Molly Ball’s willing to, though:

As the primary neared, Cochran’s campaign has sought to create the impression of a candidate fighting vigorously for survival, setting him on an intensive, two-week bus tour around the state. Unhelpfully for a man trying to defeat the image that he is more at home in Washington than Mississippi, he has sometimes sounded like an awestruck tourist, as when he told the Wall Street Journal, “It’s just good to be home, in the warmth of the friendships of people I don’t get to see as often as I would like because I’m in Washington most of the time.” And while his campaign touts his long days and punishing schedule on the trail, much of the tour has not been advertised publicly. At a coffee shop here Monday morning, I watched as Cochran’s staff moved him from place to place like a prop; Representative Gregg Harper, a supporter, had to remind him to greet patrons, and he was mostly silent as he shook hands, standing still and listening as Harper made conversation…

Onstage at the rally, Cochran read from paper notes. It was a stock speech of generic Republican lines, a marked contrast from Cochran’s rambling performance earlier in Meridian. Cochran read slowly and deliberately, looking up from the podium every so often. The other politicians surrounding him onstage appeared nervous about whether he’d make it through the text, but he did not stumble. “President Obama has taken us down some wrong paths, but starting tomorrow, we can get America back on the right path,” Cochran said. “That starts with repealing Obamacare!” Belatedly, he thrust a finger forward, then waited as the crowd applauded forcefully.

The impression you get from the piece, as someone said today on Twitter, is of a guy who might very well have wanted to retire but was conscripted into another battle by the state’s GOP establishment because he was still their best chance to stop McDaniel and maximize Mississippi’s pork opportunities. Ball calls Cochran a “Naive Establishmentarian,” an incumbent a la Bob Bennett or Dick Lugar who didn’t compete vigorously from the beginning of the race to beat back a tea-party challenge because he naively assumed that a state that had elected him repeatedly would never turn on him. Smart Republicans like McConnell, Orrin Hatch, and Lindsey Graham didn’t make that mistake and they’re all likely to be back in the Senate next year. We’ll find out tonight if the Cochran brand is enough to spare him Bennett’s and Lugar’s fate. Or maybe we won’t find out: If neither Cochran nor McDaniel gets to 50 percent, which is possible given that there’s a third-party candidate on the ballot too, they’ll head to a runoff in a few weeks.

The other big primary tonight is Iowa, where Joni “Make ‘Em Squeal” Ernst — who’s been endorsed by everyone from Mitt Romney to Sarah Palin to Marco Rubio — is the likely winner. There’s some runoff suspense there too, though, as Ernst needs to pull at least 35 percent to advance to the general election and has to hold off three opponents to do it, one of whom, Mark Jacobs, has spent millions on the race. If he ends up in a runoff with Ernst, it’ll be a battle between big money and big endorsements. And maybe some more castration ads.

You can follow the returns at Politico, RCP, or Ace’s “Decision Desk” crew, who do a nice job and have actually called races in the past before some of the pros have. The polls close at 8 p.m. ET in Mississippi and at 10 p.m. ET in Iowa.

Update: Looking good early for Cochran, says The Upshot’s Nate Cohn.

Update: At 10 p.m. ET, with 43 percent in, Cochran’s at 51 percent. He’s also up early in Rankin County, a key battleground. Cochran’s urban support is keeping pace with McDaniel’s rural support, too:

The big question about turnout remains: can the Jackson area keep up with the apparently huge rural turnout?

— Nate Cohn (@Nate_Cohn) June 4, 2014

But if Jackson has enough votes, which it probably does, these margins will be very difficult for McDaniel to overcome

— Nate Cohn (@Nate_Cohn) June 4, 2014

Update: RCP analyst Sean Trende thinks it’s looking good for Cochran, but maybe not good enough to avoid a runoff.

Update: McDaniel’s best hope:

The key seems to be whether there are enough votes left in Jones Co. (McDaniel base) to bring Cochran (R) back under 50%. Maybe/maybe not.

— Dave Wasserman (@Redistrict) June 4, 2014

Update: Hmmmmm.

Without the nursing home scandal hindering McDaniel, Cochran would very probably have lost.

— Larry Sabato (@LarrySabato) June 4, 2014

Update: Late surge by McDaniel?

Big Deal: Rankin County (largest source of GOP votes in 2012 primary) just flipped from @SenThadCochran to @SenatorMcDaniel, 50-49% #MSSEN

— Brandon (@Brand_Allen) June 4, 2014

Ace’s decision desk now has McDaniel up a tiny bit at 50.5 percent. Others have McDaniel up 49.6/48.8 with 77 percent in.

Update: McDaniel’s at 50.2 percent with 83 percent reporting. Gotta think he’s the favorite if they end up in a runoff. Now or never for Cochran.

Update: Meanwhile, no suspense in Iowa. Joni Ernst wins without a runoff, per the AP. Bring on Bruce Braley.

Update: Runoff looking more likely in Mississippi. On the one hand, McDaniel has now slipped to 49.9 percent. On the other hand:

Sen. Cochran's path to 50 percent of the vote has narrowed; sources telling me it's hard to see how he gets there now

— Kasie Hunt (@kasie) June 4, 2014

Update: Still some precincts left but it looks like we’re destined for a runoff — and an eventual McDaniel victory. Let the establishment whining begin!

I guess Mississippi doesn't want Federal money anymore. I betcha there are 49 states that will gladly take it.

— John “Open the Damn Schools” Feehery (@JohnFeehery) June 4, 2014