Hello Hillary? Goodbye, Majority
I've had an idea rattling around in my head for a couple weeks now for how to demonstrate one of my three big arguments why the Democratic Party absolutely should not nominate Hillary Clinton for the presidency next year: that her nomination would seriously endanger not just Democrats' chances of winning the White House, but also their newly captured majority in the House of Representatives. (The other two are disgust for the Two-Family Duopoly--maybe a non-starter in a culture that seems to revere celebrity ever more--and my strong suspicion that Sen. Clinton holds a similarly expansive view of presidential power that has caused so much trouble during the Bush Misrule.)

The methodological concept I'm playing with is this:

1) Of the 30 or so seats that the Democrats gained in the 2006 midterm elections, take all those who represent districts where Bush won a majority of the vote in 2004.

2) Compare the Democrat's margin of victory in his/her race last year to Bush's margin over John Kerry in '04.

3) Subtract Bush's margin from the Democrat's margin; the resulting figure is the likely 2008 margin either way with a generic Democrat against a generic Republican.

4) Measure polling response (Approve/Disapprove, "Would you consider voting for," etc) to Sen. Hillary Clinton in each district.

5) If "disapprove" is larger (and it will be), divide the difference in half and then subtract that from the figure derived in Step 3.

Example: Gabrielle Giffords (Arizona, 8th district) won her race last year by a margin of 54-42. Bush beat Kerry in that district by 53-47. Subracting that six-point difference from Giffords' twelve-point advantage, she's still up by six. But if Hillary Clinton has 45 percent approval, 55 percent disapproval in the Arizona 8th, and we divide that -10 figure in half, Giffords goes from a six-point edge to a one-point edge. If she's badly outspent (or Clinton is more disliked than I'm positing here), Giffords is very likely sunk.

Nominating Sen. Clinton will severely exacerbate the difficulties many of the first-term Democrats in somewhat hostile territory are already anticipating in their initial--and by normal historical standards, the toughest by far--bid for re-election. Already, many of them Democrats from more conservative districts have tried to inoculate themselves against the ever-looming charge of "liberalism."

[A] CQPolitics.com vote analysis underscores that some Democratic lawmakers, particularly the more centrist members of the freshman class, have been less party-line than others. Twelve of the 25 lowest party unity scores of House Democrats were registered by freshmen.

These 12 hold seats that were among the 30 captured from the Republicans last fall — and all but one represent districts that voted favored Bush for president in 2004.
...
This is not to say that these dozen Democratic freshmen are iconoclasts. They side much more frequently than not with their party on votes that divided Democrats and Republicans. Even on Iraq, before voting for the “clean” war spending bill, all of them previously voted for legislation — subsequently vetoed by Bush — that made a reduction of U.S. troops in Iraq a condition to continue funding.

Some of the dozen Democratic freshmen with the lowest party unity scores in 2007 lean to the right on some social issues. Four of them were among the 14 Democrats who voted against a bill to expand the definition of “hate crime” offenses to include certain violent crimes against an individual because of race, religion, national origin, gender, sexual orientation, gender identity or disability. Three of them joined just 13 other House Democrats in voting against legislation to promote embryonic stem cell research.

The Democratic leadership in the House is smart enough to understand that on "hot-button" social issues like abortion and stem-cell research, representatives have to vote with their districts. (It also helps that even now, enough moderate Republicans remain who will cross party lines to vote with the Democrats that the lack of support from conservative Democrats isn't generally enough to kill legislation.) Letting them go on those fights helps ensure that they'll stay on the reservation for big votes on economic and (to a lesser extent) foreign policy issues. If voters are really moved by emotional connections to their public officials, it's a good trade for the Democrats to cede a few legislative votes in exchange for preserving the sense that those officials share the values of their communities.

But the presence of a polarizing figure at the top of the ticket badly strains that perceived connection. No election is ever truly local--in that the personalities of the candidates, provincial issues, and related factors are ALL that matters--nor are they ever entirely national (in that those local factors matter not at all). In years when the presidency is at stake, however, the balance generally tips more toward the national side of the spectrum. Given how popular he remained in most of the "red" states, Bush might have helped a decent number of Republicans vying for lower office in 2004; possibly more significant was that John Kerry, or at least the caricature of him offered by the Bush political team and enabled by Kerry's own awful campaign--really hurt Democrats in those same states. The Oklahoma Senate race that year comes to mind; the Democrats ran a very strong candidate, Brad Carson, who had served in Congress for a few terms and was well within the mainstream of politics in that state, while the Republicans ran an eccentric and extremist obstetrician named Tom Coburn. Smartly, Coburn ran ads that slammed Carson as a "John Kerry Democrat"... and after months of polls showing a close race, he wound up winning by 12 points.

Carson was caught between trying to run his own race and focus attention on Coburn's many nutty qualities, and the need to keep emphasizing how he was different from his party's presidential nominee. This was a hard enough task for local down-ballot candidates with Kerry, who wasn't previously well-known (much less widely loathed) nationally. Sen. Clinton, who might be the most polarizing public figure in America (Bush can't really claim the title anymore with less than one-third of the public supporting him) is likely to have an even stronger "negative coattails" effect.

With the right opponent--pun partly intended--Senator Clinton could win the presidency with a "smarter Kerry" strategy: hold the blue states and run better races in Ohio, New Mexico, Iowa and maybe Florida. But in the states she'll write off, like Kansas and Indiana, a number of Democrats very likely will suffer defeat by association. Whether that's something Democratic primary voters are prepared to accept, I don't know--but I would like to feel more confident they're making an informed decision on the question.