JULY 20, 2009 Democrats' New Worry: Their Own Rich Voters JONATHAN WEISMAN A group of Democrats elected in recent years from some of the country's richest congressional districts have emerged as a stumbling block to raising taxes on the wealthy to pay for President Barack Obama's ambitious health-care overhaul just as the plan has begun to meet increasing resistance over its cost. Friday, two freshmen representatives -- Dina Titus, from suburban Las Vegas, and Colorado's Jared Polis, representing Boulder, Vail and some of the tonier suburbs of Denver -- joined Republicans to vote against Mr. Obama's top-priority health-care overhaul when...