Most of the background you need on the race and why it’s being watched so closely can be found in this post from last night. Establishment Republicans fear that populist candidate Kris Kobach is unelectable even with Trump at the top of the ballot this fall, as he’s lost statewide to a Democrat before and has benefited this summer from ads run by a Democratic-linked Super PAC. Populist Republicans fear that establishment candidate Roger Marshall will score an undeserving victory, propped up by money from the NRSC and Mitch McConnell’s allies in a desperate play to keep border hawk Kobach out of the Senate.

Polls show a tight race. Whichever side loses will be ticked off in the extreme. If it’s Kobach, populists will shake their fists at the NRSC: “Sons of bitches. You put a thumb on the scale for Marshall because you know he’s a robot who’ll do anything McConnell tells him. The establishment bought the nomination. You’ll pay for this.”

If it’s Marshall, establishmentarians will shake their fists at populists: “Sons of bitches. You probably just cost us the Senate. We could have had an easy win in a red state and now we’ll have to spend money there trying to drag Kobach over the finish line. Democrats bought the nomination. You’ll pay for this.”

As a bonus, the losing side will also be pissed at Trump. Kobach fans will conclude that he betrayed his populist base by refusing to endorse an acolyte who shares his views on immigration. Marshall supporters will conclude that he farted away the Senate majority by refusing to endorse a more electable candidate.

Consider it a sneak preview of the months-long melee that will engulf the entire GOP next year if Trump wipes out in November and the party has to find a way forward without him. Are the idiot Never Trumpers to blame for the party’s failures by refusing to rally to Trump’s side because they’re bitter that old-school conservatism is passe? Or are the idiot Trumpers to blame for the party’s failures by having stuck so stubbornly to a candidate who was always manifestly unfit for office? Do we need Tea Party 2.0 or do we need Trumpism Minus Trump? It’ll be real.

Polls close at 8 p.m. ET. Here’s the Decision Desk HQ where live results will be posted as they happen. As further reading on why Kobach is a bad bet, read this scathing Dan McLaughlin piece subtly entitled “Kris Kobach Is an Incompetent Loser Who Loses, and That Is Why Democrats Want Him.” I knew that Kobach’s electoral history was, shall we say, “checkered” for a populist Republican running in a reliably red state but I had forgotten all the humiliations he’s had in court and beyond trying to defend the policies he’s supported. McLaughlin didn’t.