THE CONSEQUENCES OF OPPOSING REFORM…. The conventional wisdom last week was that Democratic lawmakers from competitive districts/states would be faced with a difficult challenge: how would they explain their vote in support of health care reform?

The political establishment largely overlooked the obvious inverse — Americans have been waiting for health care reform for a long time, and there are some Republican lawmakers who’ll struggle to explain their opposition to the bill.

Take Rep. Mike Castle (R) of Delaware, for example.

This is one of the more surprising polls I’ve seen recently: Delaware Attorney General Beau Biden, son of the vice president, is leading Rep. Mike Castle (R-Del.) in a hypothetical 2010 U.S. Senate matchup. The Susquehanna Polling & Research survey has Biden beating Castle by five points. When they polled this race in April, Castle led by 21 points. (This poll was conducted from November 10 to November 15.)

What’s responsible for the Biden surge? He’s grabbed the lead in vote-rich New Castle County, built up a 41-point lead among Democratic voters, and moved to only 5 points behind Castle among independents. According to the pollster, the shift “may be a result of negative publicity [Castle] received in the state after casting a ‘no’ vote for President Obama’s health care reform bill in the U.S. Congress.”

Delaware is fairly “blue” state, but Castle has cultivated, over the course of decades, a reputation as a reasonable moderate. He’s never really faced a serious electoral threat, and when he announced his intention to run for the Senate, Castle began the race as the clear frontrunner.

But House Republicans are expected to toe the party line, and Castle has stuck with the GOP, even on odious measures like the Stupak amendment (Castle has always been pro-choice, and surely knows better). It’s apparently costing him quite a bit of support.

I don’t want to make too much of this. It’s only one poll, and it’s possible additional data will point in a more ambiguous direction. But if the poll is right, it offers an important counterweight to the notion that support for health care reform is necessarily an electoral loser, and opposition is automatically a ticket to victory.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.