Vulnerable senators seeking reelection stuck with their parties on Monday as the Senate rejected a Democratic plan to require millionaires to pay a minimum tax rate.
Republican Sens. Scott Brown (Mass.) and Dean Heller (Nev.) voted with GOP leadership to block the proposal, earning an instant rebuke from Democrats, who suggested that voters would react by ousting both incumbents in November.
Sen. Claire McCaskill, a Democrat in conservative-leaning Missouri, voted with Democratic leadership to move forward with the plan. Republicans argued it was yet another example of McCaskill voting to raise taxes.
Sen. Orrin Hatch (R-Utah), who faces serious primary challenges at a state Republican convention scheduled for Saturday, did not vote.
Only Sens. Susan Collins (R-Maine) and Mark Pryor (D-Ark.) broke with their party on the vote. Neither are up for reelection in 2012.