The percentage of House members who are NOT ideological moderates.
New data released last month by
Kenneth Keith Poole and Howard Rosenthal shows just how polemic House Republicans have become—the chart above measures the percentage of ideological purist members of the House from each party using a scoring model based on their voting records. As
Christopher Ingraham notes, the Republican party started moving aggressively away from the center around 1975 and "hasn't looked back."
This is exactly what's making it so implausible for GOP presidential candidates to win the party nomination and then stand a chance of appealing to anyone outside of their base in the general election. In a sense, the GOP has gerrymandered its way out of the presidency. Their voters are primed to vote for extremely right-wing candidates in the House who focus on a very narrow set of issues and, in turn, those voters don't want to settle for anything less in the presidential.
It's an impossible standard for any presidential candidate who wants to have even a shred of crossover appeal in the general election. And it's also the reason that even Jeb Bush—who was supposedly going to run a "moderate" primary—has now tacked right on marriage equality and Social Security, lied about the rise of ISIS, said we should "re-engage" in Iraq, and routinely defended his brother.