Congress is headed for a showdown this week over government spending, an issue that is dividing Democrats as lawmakers prepare to face voters still hurting from the recession but also angry about the huge cost of federal efforts to revive the economy. After delivering key pieces of President Obama’s first-term agenda, Democratic leaders will be turning to the more mundane work of passing budget bills and renewing tax breaks set to expire. Ordinarily, they would have little trouble drumming up votes. The