But Democrats got a reminder that Mr. Sanders, an independent and self-described democratic socialist, is not a member of their party. As Mrs. Clinton began her remarks well into the evening, hundreds of his supporters left the building to catch waiting buses or attend parties. It offended the polite sensibilities of some Iowans, and was a reminder of why he may find it difficult to appeal to the sort of mainline party activists who have backed the eventual Democratic nominee in all the contested caucuses here since 2000.
Are the Sanders folks going to walk out on the Democrats if hes not the nominee? John Deeth, a liberal blogger from Iowa City, pointedly asked on his way out of the dinner.
Unlike Mrs. Clinton and Martin OMalley, the other Democratic presidential candidate at the dinner, Mr. Sanders offered no homage, or mention at all, of Mr. Biden, a well-liked figure in the party. And he delivered a speech that he could have given in any state, making little attempt to highlight Iowa issues. Mrs. Clinton, conversely, paid homage to Iowa Democrats by name and attacked Iowa Republicans on health care.
Mr. Sanders signaled on Saturday night that he was prepared to fight. He is said to have hired a pollster for the first time this campaign, and repeatedly struck notes about areas where Mrs. Clinton has changed positions. Mrs. Clintons advisers are girding for a better-prepared version of Mr. Sanders in the next debate.
But while Mr. Sanders did use his remarks to portray the Clintons as inconsistent progressives, he could not bring himself to confront her directly the way she confronted him in their debate this month. Nor did he raise the issue of gun control, which Mrs. Clinton and Mr. OMalley discussed and which polls show could hurt Mr. Sanders in Iowa. (Mrs. Clintons Iowa brochure now includes Acting on Gun Violence as one of four issue priorities.)
A Clinton triumph in Iowa could hasten the end of the Democratic primary season. Even if Mr. Sanders won in New Hampshire, the Clinton forces would seek to frame that victory as an anomaly resulting from his hailing from a neighboring state and New Hampshires traditional affection for insurgents.
The political dynamic that has elevated Iowa, the state that haunted Mrs. Clintons White House ambitions eight years ago, could now pave her way to the nomination. The difference now, say Mrs. Clintons supporters, is that shes not running against Obama, as Iowas attorney general, Tom Miller, put it. That was a magical campaign eight years ago.