Facing a tougher than expected challenge from Senator Bernie Sanders of Vermont, Hillary Clinton’s campaign is preparing for a primary fight that could stretch into late April or early May and require a sprawling field operation in states and territories from Pennsylvania to Guam.

With the Iowa caucuses in two weeks and Mr. Sanders’s insurgent candidacy chipping away at Mrs. Clinton’s once formidable lead there, Clinton aides are acknowledging that the road to the party’s July convention could be an expensive slog. “Remember, I campaigned all the way into June last time,” Mrs. Clinton told CNN last week.

Read the article “Hillary Clinton Gets Set for a Long Slog Against Bernie Sanders” on nytimes.com.