Sioux City With less than two weeks until voting begins, the 74-year-old self-described democratic socialist Bernie Sanders could win both Iowa and New Hampshire, a once unthinkable outcome in a primary campaign that was supposed to be tailor-made for Hillary Clinton.
"Today the inevitable candidate doesn't look quite so inevitable," Sanders told voters on Tuesday.
The Vermont senator's down-to-business demeanour on the campaign trail has been met with youthful enthusiasm during his unexpected rise in the Democratic race for president.
While Sanders first drew attention for the overflow crowds he drew around the country last summer, he's making more intimate appeals to voters in the final few days before the Iowa's February 1 caucuses.
As voters filed into events where Sanders made his pitch for increasing the federal minimum wage to $15 per hour and breaking up big Wall Street banks, a campaign soundtrack played a heavy rotation of songs touting revolution. Sanders has called for a "political revolution" in America.
Young people with nose rings and green and purple tinted hair filled the seats directly behind the candidate, though the rest of the audience was older.
Sanders, an independent who caucuses with Democrats on Capitol Hill, began his campaign with firm rules about what he was not willing to do to win the presidency. He's among the most vigorous critics of super political action committees, groups that can accept donations of any size, and frequently touts his campaign's reliance on small donations.
He also vowed to avoid negative, personal attacks on his rivals. But with the prospect of victory in the early states at hand, Sanders is testing the limits of that pledge.
In addition to his comments on Clinton's evaporating inevitability, he points out the big-money speaking fees Clinton received from Goldman Sachs, the Wall Street giant that's a frequent villain in Sanders' speeches.
While Sanders may be striking a chord with voters seeking an outsider candidate, he's also a practised politician.
Taking a page out of Republican front-runner Donald Trump's playbook, Sanders has recently started opening his remarks with lengthy references to his improving poll numbers. He's particularly focused on surveys showing he's more likely to beat Trump in the general election than Clinton, showing his irritation with suggestions from within his own party that's he's unelectable.
Sanders also knows he lacks foreign policy experience, particularly next to Clinton's four years as secretary of state. So he reminds voters of Clinton's vote in favour of the 2003 invasion of Iraq.
Even if Sanders can turn his momentum into victories in Iowa and New Hampshire, there are daunting challenges ahead. He's less well known among minority populations, which some Democrats see as a vulnerability for him as the race heads to states with more racially diverse populations.
Sanders is making an effort in South Carolina in particular to reach out to black voters, hoping they'll see the rumpled, ageing socialist as their advocate.
"This is it. Here I am," Sanders said as he closed an event in Iowa. "For better or worse."