When it comes to policy, moderate politicians keep their mouths shut, says Stanford political scientist

Looking at senators' portrayals of themselves, Stanford political scientist Justin Grimmer found two basic strategies: More extreme candidates talk policy. More moderate candidates talk pork.

Lawrence Jackson / White House President Obama delivering an address to a joint session of Congress at the U.S. Capitol

President Barack Obama delivers an address to a joint session of Congress at the U.S. Capitol on Sept. 9, 2009.

Where are all the moderate voices? In a country that's supposed to be more or less centrist in its views, the moderates' relative absence from the national political conversation is surprising.

The issue isn't that they don't exist. Centrists like Scott Brown (R-Mass.) and Claire McCaskill (D-Mo.) feature prominently in the current Senate campaigns. But Brown has consistently avoided the question of national politics. And McCaskill, as Missouri news organizations pointed out, was reluctant to comment on issues like the recent Supreme Court health care ruling. The issue, in other words, is that moderates don't talk about issues.

According to Stanford political scientist Justin Grimmer, senators from swing districts, who tend to be moderates, prefer to emphasize the federal money they've brought to their districts without mentioning national issues.

This strategy leaves the ideological debate to the more radical representatives who tend to represent heavily Republican or Democratic areas.

"When you hear about policy, it tends to be from the extremes of the party, not the moderates," said Grimmer.

The result? An artificially polarized conversation.

Credit vs. issues

Grimmer, an assistant professor of political science, studies representatives' "home styles" – the ways in which legislators choose to portray themselves to their constituents. Often this portrayal is, not surprisingly, more important than a senator's actual performance.

"In American democracy, a big part of voter evaluation of legislators' performance happens on the legislators' terms," said Grimmer.

In a forthcoming research paper on the subject from the American Journal of Political Science, Grimmer analyzed every Senate press release from 2005 to 2007 with a statistical model that identifies the topic of each press release.

He found that senators from strongly Democratic or Republican states put out more releases devoted to issues. Senators from marginal districts emphasized appropriations.

The effect can be quite strong. During the Bush presidency, liberal Democrats were five times more likely to mention the Iraq war than moderate Democrats.

As for the moderates and their appropriations, it turns out that they're not as good at pork as you might think.

As Grimmer points out in another study, coauthored with Stanford communication PhD candidates Solomon Messing and Sean Westwood, forthcoming from the American Political Science Review, a senator's success as a "credit claimer" is associated with the number of times he or she takes credit for an appropriation, rather than the amount of money appropriated. And senators frequently take credit for appropriations they weren't responsible for.

Polarized maps

To some extent, said Grimmer, this divide between the two styles is due to the fact that American politicians are more beholden to their local electorate than to their parties. Unlike a parliamentary system, in which centralized parties run lists of candidates, the American system involves individual candidates running separately for each position in each district.

"It seems like parties are willing to tolerate people who don't adopt the party message if those senators are able to contribute to the party's votes in Congress," he said.

The situation has been exacerbated recently by the political homogenization of congressional districts and states. As Americans increasingly choose to live in communities with people like themselves, fewer and fewer congressional races are close calls.

In every election from 1998 to 2008, no more than 15 percent of House races were decided by less than 10 percentage points. (The 2010 elections were a change – for the first time since 1992, marginal winners made up a quarter of the House. But there's little reason to believe that this trend will continue.)

"If we had more heterogeneous districts, maybe we would see more moderates participate in discussions," said Grimmer. "But districts aren't becoming more heterogeneous."

Click here for more insight from Stanford researchers into the 2012 elections.

Justin Grimmer, Political Science: (650) 723-3156, jgrimmer@stanford.edu

Max McClure, Stanford News Service: (650) 725-6737, maxmc@stanford.edu