WASHINGTON — Former Vice President Joe Biden and Sen. Bernie Sanders sought in Sunday’s Democratic debate to cast themselves as best-positioned to lead the nation through a global pandemic, with Biden pledging to deploy the military to help with recovery efforts and Sanders using the crisis to pitch his long-sought overhaul of the country’s health care system.

The fast-moving novel coronavirus 2019 dominated the first one-on-one faceoff of the 2020 campaign, reflecting the way the crisis has upended American life by closing schools, disrupting travel and raising questions about President Donald Trump’s ability to lead the nation through turbulent times.

Biden’s and Sanders’ prescriptions for addressing the public health and economic crisis highlighted the ideological divide between the two men vying for the Democratic nomination. Biden, a centrist who helped implement the 2009 bailout of the financial industry, warned that another government-backed economic rescue plan may be needed in the coming months, while the liberal Sanders suggested a tax on the wealthiest Americans.

The stakes and the standings in the race for the Democratic nomination have shifted dramatically since Biden and Sanders last debated less than three weeks ago. After a sluggish start to the primary season, Biden has surged to the front of the field, drawing overwhelming support from black voters and consolidating the backing of several rivals who have dropped out of the race.

Sanders has struggled to broaden his coalition beyond young people and liberals and is quickly running out of time to regain momentum. Facing the prospect of more losses in contests on Tuesday, Sanders appeared focused on using Sunday’s debate to vigorously pitch the sweeping government-backed domestic policy programs he has touted throughout his decades in politics.

He focused in particular on health care, reviving a now-familiar debate within the Democratic Party. Sanders argued that the troublesome shortages in coronavirus tests and growing anxiety among Americans highlights why the U.S. should move to the government-run, “Medicare For All” system he has long championed.

“One of the reasons that we are unprepared, and have been unprepared, is we don’t have a system. We’ve got thousands of private insurance plans,” said Sanders, who backs a sweeping government-run health insurance program.