The biggest continuing story in Congress has been the ability of Tea Partyers and other movement conservatives to keep relatively moderate Republicans from defecting from their version of the party line, no matter what that line might be. That’s why my vote for the big political news of the past few days are the two polls showing that Indiana Republican Sen. Richard Lugar is engaged in a tight battle for re-nomination.

This is very simple: As long as Republican politicians in office believe that losing their seats via a primary battle to Tea Partyers is a greater risk than losing it to a Democrat in November, they’re going to have a powerful incentive to vote for whatever wacky things movement conservatives can dream up. If you’re a Republican senator or member of the House, you are certainly aware of Bob Bennett, the longtime conservative Republican from Utah who suddenly wasn’t conservative enough in 2010 and was defeated by Mike Lee. You’re probably also aware of Lisa Murkowski’s loss in an Alaska primary election (although she wound up running and winning anyway in the general election), and even Mike Castle’s loss in a primary to Christine O’Donnell — sure, Castle’s case wasn’t exactly the same since he was trying to move from the House to the Senate, but for skittish politicians, it was close enough.

Republican legislators also may also be aware of how John McCain survived a similar scare by moving sharply to the right. And they don’t have a whole lot of obvious counter-examples recently of Republicans who moved to the right and were then defeated in November.

Of course, that’s a short-term perspective; one could note that there are plenty of incumbent Republicans who lost in 2006 and 2008. Rick Santorum, anyone? But that’s the point: The example of Bob Bennett might fade rapidly if it’s not reinforced in each election cycle. Lugar doesn’t even have to lose to make the message clear; a good, solid scare is probably enough.

Which is why these two polls matter. With the news that it’s a close race, the real goal of the primary challenge — keeping the fear alive — is already at least partially met, no matter what happens from here on out. That means more party-line voting from Republicans in Congress and more influence to those who get to define what “conservative” means within the GOP.