The NBC News Political Unit has put together a briefing book for Election Day; a guide for users to better understand the upcoming  presidential, Senate, House, and gubernatorial contests.

This nearly 150-page guide offers the NBC News battleground map, information on the most important ballot measures to watch, ad spending tallies, voter turnout history, and past election results.

It also includes an hour-by-hour viewer's guide to the top races in each state, and ponders the question, "What if there's a tie?"

Click the image or click here to check it out.

According to a spokesman at the Texas Republican Party, a member of the Texas GOP’s executive committee drafted an email to call an emergency meeting to revisit its delegate-allocation rules.

And make no mistake: This effort is coming from Santorum world.

Santorum, in fact, commented on this subject yesterday while campaigning in Pennsylvania.

“After Pennsylvania, the calendar in May looks very, very interesting -- a lot of strong conservative states who are looking for the opportunity to tighten this race back up. There's talk now of maybe making the state of Texas, 154 [sic] delegates, a winner-take-all state. We would like that. That would be a good thing.”

And today on MSNBC's "Andrea Mitchell Reports," Santorum spokeswoman Alice Stewart added, “Keep an eye on Texas, that’s going to be critical in terms of how the votes play out there, whether it’s winner-take-all or proportional. Texas will be critical in the primary election and everyone needs to pay attention to that."

Right now, Texas is set to award its 155 delegates -- on May 29 -- proportionally. But making it winner-take-all could help Santorum narrow Romney’s delegate lead, if Santorum remains in the race (and more importantly, if he remains competitive).

Per the Texas GOP’s bylaws, you need 15 members of the executive committee to call such an emergency meeting.

And it takes a two-thirds vote at that meeting to propose a rule change -- that would later be sent to the Republican National Committee.

But a Republican official says the RNC is "unlikely" to grant Texas a waiver to change its rules.

"If they succeed in changing the rules in Texas, then they have to come to [the RNC] for a waiver, and it is unlikely to happen."

All eyes are on the GOP hopefuls who are facing Iowa caucus-goers in the first nominating contest of the 2012 race.

The NBC political team will be live-tweeting the caucuses, offering minute-by-minute updates and analysis.

Tweets from NBC producers, embeds, and correspondents will appear in this post throughout the evening.