DES MOINES — The race between Hillary Clinton and Senator Bernie Sanders, which voters will begin deciding a week from Monday, is not just about the White House anymore. It has intensified into an epochal battle over their vastly different visions for the Democratic Party.

Mr. Sanders, a New Deal-style liberal from Vermont, last week became the party’s first top-tier candidate since the 1980s to propose broad-based tax increases. He argues that only muscular government action — Wall Street regulations, public works jobs, Medicare for all — will topple America’s “rigged” economy.

“Something is grotesquely wrong in America,” he said Thursday in New Hampshire, urging voters to deliver a landslide in November that would cow Congress into enacting his agenda.

Mrs. Clinton, a mainstream Democrat, has started contrasting herself with Mr. Sanders by championing a “sensible, achievable agenda” and promising to build on President Obama’s legacy in health care, the economy and national security. She is the classic continuity candidate: seeking support from blacks, Hispanics, women, union members and suburban voters, and proposing policies that are friendly to families and businesses — strategies that have defined the party since President Bill Clinton’s election in 1992.