(Oct. 12) For most congressional Republicans, opposition to the Affordable Care Act is a simple matter of political math.
The latest data by American Community Survey, which tracks demographic trends, help explain why some Republicans in Congress so readily attack Obamacare, and why Democrats adamantly support it.
Although there are notable exceptions, Democrats represent most districts where the greatest numbers of uninsured residents reside. Republicans, in turn, need not rely on the votes of the people who lack health insurance and would gain most from Obamacare.
That's especially true in parts of California and Texas, where the heaviest concentrations are of people without health insurance. Those districts are heavily populated by Latinos and African American voters, not part of the Republicans' base of voters.
The 10 congressional districts with the largest percentage of uninsured residents are held by Democrats. Two in Los Angeles are represented by Reps. Xavier Becerra and Lucille Roybal-Allard. Two others are in Florida. Six are in Texas.
The survey shows that 39 percent of the residents under 65 in Becerra's district lack insurance, second only to a Dallas-Fort Worth district, where almost 41 percent of the residents have no insurance.
"Folks in my district are very hard-working, out there hustling," Becerra told me. "They work hard, but they are living in expensive Los Angeles, and it's hard for them to afford health insurance."
There are, of course, exceptions. Rep. Henry Waxman, a Democrat, represents a congressional district on the west side of Los Angeles with the smallest percentage of people under 65 without insurance, 10.1 percent. Waxman was an architect of the Affordable Care Act and one of its big defenders.
There are relatively high numbers of uninsured residents in Rust Belt states, including some Republican districts. Becerra noted that workers and employers there find it increasingly difficult to afford insurance, which is an argument for Obamacare, though not one that Republicans accept.
House Republicans are demanding that President Barack Obama negotiate the Affordable Care Act, his signature domestic achievement, in exchange for agreement to continue funding the federal government. Predictably, he has refused, and the federal government went into partial shutdown Oct. 1.
By most estimates, there are about 30 or 32 hard-core Republican supporters of the shutdown. Two-thirds are from Southern states.
Most are like Iowa's Steve King, one of the most outspoken supporters of the shutdown. He represents a district where 10.5 percent of the residents under 65 are uninsured, lower than all but 64 of the 435 congressional districts.
There also are Republicans who represents districts with large concentrations of uninsured, particularly in Texas, where five hard-line congressional Republicans represent districts where at least 20 percent of the residents don't have health insurance.
Rep. Louis Gohmert, a Republican who represents northeastern Texas, calls the "Obamacare calamity" a "national nightmare." A fourth of his constituents have no insurance. It's also one of the nation's safest Republican districts. Gohmert won re-election last year with 71 percent of the vote.
Andrew Wheat, research director at the liberal advocacy group Texans for Public Justice in Austin, cited Texas' partisan gerrymandering as one reason why Republicans can be so bold.
Uninsured residents probably don't vote for Republicans. But Republicans still can easily control the outcome on Election Day, thanks to gerrymandering.
"These districts are designed to have manageable numbers of minorities," Wheat said.
The one Californian who is among the hard-liners fanning the shutdown is Rep. Tom McClintock, R-Elk Grove, whose district includes Yosemite and Kings Canyon national parks, both of which are shuttered as a result of the shutdown.
Opposition to Obamacare is an easy stand for McClintock to take. American Community Survey found that a mere 15 percent of his constituents are uninsured. And more Republicans live in his district than any district in the state, 189,520.
The firm Political Data Inc. also noted that more than a fourth of the registered voters in McClintock's district are 65 or older. Since Medicare provides their health care, they don't need what the Affordable Care Act can provide.
While McClintock pushes the shutdown, Rep. David Valadao, a first-term Republican who represents parts of Kern, Tulare, Fresno and Kings counties, is one of the 40 congressional members who embrace the call by the moderate No Labels group for a compromise.
The Democratic Congressional Campaign Committee is targeting Valadao, for obvious reasons. There are 30,000 more Democrats in his district than Republicans, and 28 percent of the residents under 65 lack insurance, 26th worst in the nation.
For Valadao, the math is clear: Reopen government and end talk of defunding the Affordable Care Act. For hardliners in his party, however, the numbers make clear they can fight on.
Follow Dan Morain on Twitter @DanielMorain.