Analysis: The political perils Bernie Sanders poses for Hillary Clinton

Susan Page | USA TODAY

Show Caption Hide Caption Bernie Sanders to announce presidential run | Why It Matters USA TODAY's Washington Bureau Chief Susan Page explains four reasons why Bernie Sanders's presidential run matters.

WASHINGTON — He's a 73-year-old populist with a chaotic halo of thinning white hair who isn't, technically, a Democrat. The last political party he joined was the Liberty Union Party a generation ago to oppose the Vietnam War.

But Vermont Sen. Bernie Sanders, slated to announce Thursday that he will seek the Democratic presidential nomination in 2016, poses some significant political perils for Hillary Clinton — even though she's in such a strong position to win the nomination that "front-runner" doesn't quite do justice to the dominance of her standing.

Sanders, the longest-serving independent in congressional history, is positioned to tap the vocal resistance to Clinton among those in the Elizabeth Warren wing of the Democratic Party, since the Massachusetts senator herself insists she's not jumping into the race. He comes across as earnest, authentic and accustomed to the person-to-person campaigning favored in small states like his own and in Iowa and New Hampshire, states with the opening presidential contests.

And he will provide pressure on Clinton from the left on such issues as free-trade pacts, Wall Street regulation and Social Security.

Sanders is a leading opponent of the Obama administration's 12-nation Pacific trade pact; Clinton called it the "gold standard" when she was secretary of State and has dodged questions lately about whether she supports it now. He argues Wall Street banks have too much power; she has received millions of dollars in contributions and speaking fees from Wall Street interests for her campaigns, the Clinton Foundation and herself.

On Social Security, Sanders in an op-ed article in The Des Moines Register Wednesday called for raising payroll and investment taxes on the affluent to finance an increase in benefits for the elderly.

Then there's Clinton's vote in 2002 to authorize the Iraq war, which provided a critical opening for Barack Obama's challenge in 2008. Sanders, then a member of the House, voted against the authorization. Given the continued turmoil in Iraq, it's no favor to Clinton to be reminded of her early support of the war there.

Sanders is the first challenger to Clinton, but he's not likely to be the last. Former Maryland governor Martin O'Malley, former Virginia senator Jim Webb and former Rhode Island governor Lincoln Chafee also are weighing campaigns.

All that said, even Sanders' top strategist doesn't sound optimistic that it is possible to deny Clinton the 2016 nomination.

"Possible?" repeats Tad Devine, who was an adviser to the presidential campaigns of Al Gore in 2000 and John Kerry in 2004. He has worked for Sanders since 1996, through a half-dozen House re-elections and two successful Senate runs. "I'll say 'possible.' I'm not going to go much beyond 'possible.' I'm not going to deny for a second she is as strongly situated as any non-incumbent candidate who has sought the nomination of a major political party in my lifetime.

"But going back to Lyndon Johnson, you can change the calculus of an election, if you fit the times," he adds. The long-shot anti-war challenge by Minnesota Sen. Eugene McCarthy helped convince President Johnson not to seek renomination in 1968. "Can you come forward and resonate with people?"

Sanders aims to raise $50 million in small, online contributions to finance campaigns in Iowa, New Hampshire, Nevada and South Carolina, and to get on the ballot in succeeding states, Devine says. If he does well in early contests, the theory goes, that will fuel a flood of contributions to continue. A PPP Poll of Iowa Democrats released Tuesday had Clinton at 62%, Sanders in second at 14%.

Veteran Democratic pollster Mark Mellman is skeptical about his prospects against Clinton, who he says is in a much stronger position that she was in 2008.

"Bernie Sanders is a great senator and a wonderful man, but he, and all of her other putative opponents, are in a vastly weaker position than Barack Obama was at this time eight years ago," Mellman says. "Her opponents will no doubt keep her on her toes, but she will almost certainly keep them underfoot."

Of course, that could be a recipe to trip.