Back in April, I wrote a piece arguing that the Democrats would have trouble governing despite their large majorities in both Houses of Congress. My theory was that because so many Democrats hail from Republican-leaning districts, Democrats would struggle to cobble together majorities on contentious issues that divided along partisan lines.

The recent vote on so-called “Cap and Trade” legislation demonstrates this difficulty. It only passed narrowly: 219-212. Eight Republicans voted for the bill, while forty-four Democrats voted against it.

If you haven’t already read Jay Cost’s analysis of the vote, you should go do so now. Jay carefully analyzes the House vote by state, and compares it to Senate seats in those states. This allows him to conclude that the climate change bill faces long odds in the Senate.

But as I look at the map Jay created, something else jumps out at me. The map is Bush v. Gore, with a few exceptions. The Congressional districts from blue states supported the bill; the Congressional districts from red states opposed it.

Now this isn’t entirely surprising: Blue states have more Democrats at the congressional level. But some states with Democratic dominated delegations nevertheless opposed cap-and-trade: Pennsylvania, West Virginia, the Dakotas, Mississippi, Arkansas and Indiana, to name a few.

What we see is that the Democrats who came from Republican-leaning states and districts tended to vote like Republicans on this controversial piece of legislation. As I explained in April, this doesn’t make them “bad Democrats.” It is just that these legislators must be able to make the case every two years that they have stood up for their constituents’ interests, or they will be fired. And a party change does not change the makeup of the constituency.

Consider the following chart. It shows the 68 Democrats who occupy districts with Cook Partisan Voting Index ratings of R+1 or greater. To keep the chart from scrolling too much, I’ve “double-columned” it. Democrats who voted “no” on Waxman-Markey are highlighted in red.

About half of the Democrats representing Republican-leaning districts voted “no.” Looking at the chart, we can see that the closer the district came to the mean, the more frequently Democrats begin voting “yes.” Only four Democrats in districts with PVI’s of R+10 or more voted “yes”: Skelton, Gordon, Kratovil, and Boucher. Three of the four are well-entrenched Democrats who will only regret this vote if things truly head south for the Administration (it was an especially risky vote for Boucher, who represents a coal-producing region). Kratovil hails from a coastal district where environmental concerns remain high.

Only eight Democrats with Democrat-leaning PVI’s voted “no.” Barrow (D+1), DeFazio (D+2), and Costello (D+3) all represent districts that only slightly lean Democratic, Davis (D+18) is preparing for a statewide run in a red state, Viscloskey (D+8) represents a major industrial center, and Stark and Kucinich probably thought the bill was too weak.

Now let’s look at the Republicans. This is easy; there are only eight from Democratic-leaning districts.

Again, about half of these Republicans voted “yes” on Waxman-Markey. The remaining members – Bono Mack (R+3), Lance (R+3), McHugh (R+1) and Smith (R+6) – all come from marginal districts that Obama carried or came close to carrying.

What does this mean for the Democrats and Republicans? Well it is good news and bad news for both parties. The bad news for Democrats is that they haven’t succeeded in breaking Republican ranks on controversial legislation. For every Republican that breaks ranks, it is one more Democrat from a marginal district who can vote “no,” so by more-or-less sticking together, Republicans limit the number of Democrats who can vote “no.”

This is important. In 1994, Republicans defeated 34 Democratic incumbents. Of those, only five had voted against the 1993 Clinton budget. No Democrats who voted against both the 1993 budget and the 1994 Crime Bill (which included the assault weapons ban) lost. Two-thirds of the Democrats who lost had voted for both pieces of controversial legislation.

This is not to say that every Democrat from a red district who voted for cap-and-trade will lose. Democrats like Tom Bevill, John Tanner, and Paul McHale voted for the Clinton budget and survived in red districts. But as the blue votes pile up in red districts, they take their toll. Almost all Democrats are now on record voting for the stimulus and Obama’s budget. Now many Democrats from red districts have also voted for Waxman-Markey.

It isn’t clear what they get for this, politically at least. The most recent available data show that only 29% of Americans consider “the environment” to be “extremely important.” 70% consider the economy to be “extremely important” and 43% say the same about taxes. Only 5% consider “energy and the cost of gas” to be the most important issue facing the country. To the extent Republicans succeed in branding Waxman-Markey as anti-job and anti-growth, the Democrats’ protestations that it helps the environment will likely not get them very far. The Republicans argument will be stronger if unemployment is still hovering around 10% in November of 2010.

The problem for Republicans is that the Democrats’ margin is large enough that many of their most vulnerable members can vote against controversial legislation, and that legislation will still pass. Republicans would have loved to have seen Democrats like Childers, Davis, Mollohan and Dahlkemper forced to choose between a signature piece of legislation for the Obama Administration and their seats. But elections have consequences, and this greater flexibility for the Democrats makes it much more difficult to pigeonhole Democrats as reflexive supporters of the Administration.

Of course, Waxman-Markey probably has the biggest problems. If we assume that the Senate will break in roughly the same way as the House (a big assumption, but probably good enough for a spitball estimate), we can look at the statewide PVI and expect half of the Republican PVI Democrats to vote “no” and half of the Democratic PVI Republicans to vote “yes.” We would then expect nine Democrats to vote “no” and three Republicans to vote “yes,” which puts the bill an awfully long way from the 60 votes it will need.