House Democratic leaders were struggling Thursday to contain uprisings on the hot-button issues of abortion and immigration that have left them little margin for error as they attempt to push through a massive health-care reform bill this weekend.

Although confident of victory, House Speaker Nancy Pelosi (Calif.) and other Democratic leaders were working to limit defections to the roughly 25 Democrats viewed as "hard no" votes. There will be 258 Democrats in the House by the time the vote takes place, but to secure the 218 votes needed for passage -- and with prospects dim for Republican converts -- Pelosi can afford to lose no more than 40 members of her caucus. President Obama had been slated to head to the Hill on Friday to push wavering Democrats to get behind the...