Storyline we’ll be watching tonight:

Cruz’s Margin. Every recent poll but one has shown U.S. Sen. Ted Cruz with a lead over Donald Trump that is at least at the upper end of the margin of error, and Marco Rubio finishing third by double digits. We’ve noted that the sampling methods of some of these polls indicate differences of opinion when it comes to figuring out exactly who is going to the polls. Cruz did not finish first in his 2012 primary for U.S. Senate against then-Lt. Gov. David Dewhurst and others. In fact, he received a little over 34%, which put him 10 points behind. Cruz will almost certainly increase his vote total over that primary, but can he increase his vote percentage to at least 40%?

Down-ballot Drop-off. A significant number of primary voters cast a ballot for their preferred presidential candidate and no one else. As turnout increases, the drop-off of voters down the ballot increases. In 2008, a record number of people cast ballots in the Democratic primary, but nearly a quarter of them voted only for president. Almost 700K did not vote in any other race, and the drop-off got bigger the farther one goes down the ballot. Who this helps and hurts is unclear, but consider that neither Cruz nor Trump could be classified as an “establishment” candidate. If a whole lot of people come into the Republican primary for the first time, and vote only for either of these candidates, then the anti-establishment coattails are not as strong as they could be. This effect may matter in some close races between anti-establishment (in other words, anti-Joe Straus) candidates and their more establishment-esque opponents.

Tea Party Ceiling. How do Tea Party candidates do when a rush of non-primary voters reduces the overall influence of the Tea Party bloc of voters? With record Republican turnout all but assured, this primary ought to provide insight as to whether the Tea Party has a ceiling, and, if so, what is it? However, this line of thinking assumes that the incoming voters are more moderate as a group than the “regular” primary voters. What if that’s not the case?

We assume that Cruz’s voters will be more inclined to vote for anti-establishment, Tea Party candidates where possible. What about Trump’s? As far as we can tell, candidates have not been specifically targeting Trump supporters. The Tea Party’s leaders have been outright hostile toward him. Do they stick with the anti-establishment leanings of their presidential candidate as they go down the ballot, or do they turn against specific Tea Party folks who have backed Cruz, or do they vote a bit more randomly?

Cruz ought to receive more votes today than he has in previous races here. But the third or so of voters who support Trump represent a potentially huge wildcard, especially if they’re new to the primary and vote a full ballot.

Fallen Incumbents. Since 2002, an average of six incumbent state representatives has lost their re-election bids in the primary, and an average of two incumbent state representatives have been forced into runoffs (where they mostly lose). The Republican primary features numerous battles between Tea Party, anti-establishment candidates (and incumbents) facing off against candidates who are more likely to fit the “establishment” model. The Democratic primary features a few races where single-issue interest groups are providing significant funding in efforts to topple incumbents. Only six incumbents could be forced into runoffs, but there’s a good chance that a runoff looms for at least one of them.

Sen. Jose Menendez

Sen. Jose Menendez

Grudge Matches. Three special election rematches are on the ballot today, led by the SD26 re-battle between Sen. Jose Menendez and Rep. Trey Martinez Fischer. Menendez won the special runoff election with the help of voters who do not typically vote in Democratic primaries. In HD17, Brent Golemon is trying to reverse the special runoff election win by Rep. John Cyrier. Also in San Antonio, a pair of challengers are trying to reverse their respective out-of-the-runoff finishes against Rep. John Lujan and his runoff opponent, Tomas Uresti.

There are seven rematches of past primary elections. Since 2002, the loser of the most recent battle has won 12 of the 28 rematches. Three of these rematches involve former representatives seeking to reverse the 2014 primary. Since 2002, former representatives have won five of eight primary rematches.

In three other districts, former representatives are trying to win their way back into the House against opponents they have not faced before. In HD55, former Rep. Hugh Shine is trying to return to the House after a 13-term absence, something that hasn’t been done since 1938.

Congressional Angst. Sitting U.S. House members don’t fall in primaries very often, but several are feeling a little more heat than usual, led by U.S. Rep. Gene Green, who faces the Latino former Harris Co. Sheriff in a Latino-majority district. Several Republicans face Tea Party challengers in a year when anti-incumbent sentiment appears to be higher than most.

Runoffs Likely. Statewide runoffs are likely for Railroad Commissioner and at least one Court of Criminal Appeals seat, and numerous legislative runoffs are expected as many open-seat races are likely to end without outright winners tonight. Candidates with the most money generally advance to runoffs, but several lesser-funded candidates have endorsements from influential groups that have, in the past, swung elections from better-funded rivals. In 2014, two dozen candidates defeated, or advanced to runoffs over, candidates who raised more money.

We expect it to be a long night.