Sanders has deployed about 50 paid campaign aides apiece to Nevada and South Carolina, the next two states on the calendar, according to advisers. Paid staffs are on the ground in all of the 11 “Super Tuesday” states that have contests on March 1, a presence that appears to at least match that of the Clinton camp.

The Vermont senator is also airing TV ads and Spanish-language radio spots in Nevada. He is about to go on TV in South Carolina. And his team is mapping out plans to spend a fresh wave of small-dollar donations expected to arrive if he upsets Clinton in Iowa or New Hampshire, as recent polls indicate is possible. That money, aides say, would allow Sanders to compete with the former secretary of state and Democratic front-runner in the crush of contests that quickly follow on the calendar, as the playing field rapidly broadens and the election becomes more dependent on expensive television ads.

The preparations are part of an effort to buck what has emerged as the latest conventional wisdom surrounding the Democratic contest: that even if Clinton loses the first two contests, her superior campaign infrastructure and other advantages — including the demographics of the electorate — will allow her to overpower Sanders in subsequent states.

“There will absolutely be a very active contest after the first two states,” said Sanders’s campaign manager, Jeff Weaver, who disputed the oft-repeated notion that Clinton has a “firewall” in states that follow Iowa and New Hampshire. “A lot of time and effort have gone into developing our plans for the states beyond the first four.”