Republican leaders have intensified their planning to prevent a government funding shutdown, weighing legislative options that would redirect GOP anger at Barack Obama's expected action on immigration and stave off a political disaster, according to sources involved with the sessions. Obama plans to use his executive authority to change the enforcement of immigration laws by the end of the year, a move that top Republicans warn could derail efforts to pass a long-term spending bill by a Dec. 11 deadline. Increasingly, some top Republicans believe that it will be difficult to pass the year-long spending package that they originally envisioned,...