Jeb Bush, former governor of Florida, reacts during a keynote speech session at the National Automobile Dealer Association (NADA) conference in San Francisco, California, U.S., on Friday, Jan. 23, 2015. Photographer: David Paul Morris/Bloomberg

There is something about today's Republican Party. The grass-roots base -- call it the "tea party" if you must -- simply loves to joust with the party establishment.

And nowhere is that more the case than in the first contest of the 2016 presidential election: the Iowa caucuses.

Witness this new Bloomberg Politics/Des Moines Register poll of 2016 caucuses. The big takeaway Sunday was that Wisconsin Gov. Scott Walker has taken the lead (a statistically insignificant one, albeit). More specifically, the big takeaway was that the erstwhile front-runners -- Mitt Romney and Jeb Bush -- don't lead. (The survey was conducted before Romney announced Friday that he won't run.)

The reason: The Iowa caucuses just aren't friendly to establishment Republicans.

We noted Friday that Romney's unfavorable rating among likely caucus-goers was 40 percent -- a very high number, given that these are members of Romney's own party.

Well, he's not the only one. While Romney's favorable/unfavorable split is 57/40, Bush's is even worse: 46/43. And New Jersey Gov. Chris Christie's image is downright bad: 36 percent favorable vs. 54 percent unfavorable. Again, this is among Republicans.

Other, less establishment-oriented Republicans don't have this problem. Sen. Rand Paul (Ky.) is at 64/25. Former Arkansas governor Mike Huckabee is at 66/28. Walker is an unparalleled 60/12. None of the Democrats have this problem, either; Hillary Rodham Clinton is at 84/15, Vice President Biden is at 78/20, and Sen. Elizabeth Warren (Mass.) is at 58/11.

The reason voters are picking on Romney, Bush and Christie? It's because they are perceived as too moderate. Thirty-seven percent each say Romney and Bush are too moderate, while 46 percent say that about Christie. Nobody else comes close.

This is precisely why the caucuses picked Huckabee in 2008 and former senator Rick Santorum (Pa.) in 2012. It's why Sen. John McCain (Ariz.) didn't compete in 2008 and why Romney almost didn't in 2012. Establishment support means far less here.

Bush sounds as though he'll compete in Iowa. While he skipped the Iowa Freedom Summit last weekend, he has hired well-known Iowa GOP operative David Kochel as his senior strategist and potential campaign manager.

But if you're Bush -- or Christie -- these numbers have to color your strategy going forward. When about half of likely caucus-goers already have decided that they don't like you a year before the caucuses, getting them to vote for you is going to be exceedingly difficult.