Most important West Virginia Democrats will skip Democratic National Convention

Just curious, but why are these guys Democrats?  If he also doesn't like Romney, why not run as an independent?  Given that the Democrats in the Senate go with Obama virtually all the time, isn't he really supporting Obama's policies by caucusing with the Democrats? From The Hill newspaper:

Three prominent West Virginia Democrats said Monday that they would skip the party's national convention in Charlotte, N.C., this September over concerns that links to the party could hurt their re-election chances.  Sen. Joe Manchin, Rep. Nick Rahall, and Gov. Earl Ray Tomblin all said they would avoid the convention, according to the West Virginia Metro News.
"I intend to spend this fall focused on the people of West Virginia, whether that's representing them in my official U.S. Senate duties or here at home, where I can hear about their concerns and ideas to solve the problems of this great nation," said Manchin in a statement. "I will remain focused on bringing people together for the next generation, not the next election."

UPDATE: Fox News piece:

three other members of Congress have also distanced themselves from the convention -- and by extension the president -- by announcing their intention not to attend. They include Pennsylvania Rep. Mark Critz and New York Reps. Bill Owens and Kathy Hochul, both of whom won special elections in recent years.
"I guarantee that my time will be better spent meeting the farmers, small business owners and other people who put me here," Hochul said in a recent interview with The Daily. . . .
"One of the problems for a Democratic president or any Democratic candidate is that sometimes pleasing one of your core groups can displease another,” he said. As an example, Barone points to the intra-party fight over gay marriage. "Young voters are heavily in favor of it. Black voters have tended to be heavily against it." . . .