ANALYSIS: Why Michelle Obama and Bernie Sanders Are Key to Hillary Clinton's Chances

— -- Here come the reinforcements.

Michelle Obama and Bernie Sanders hit the campaign trail today for Hillary Clinton. Their separate events would be easy enough to miss in the blur of political news, particularly in the wake of the first general-electionpresidential debate.

But those unlikely supporters are critical to the Clinton campaign’s efforts to solidify and energize the Democratic base this fall. The two former political foes of the Democratic presidential nominee hold distinct but distinctly important appeals for voters where Clinton has significant weaknesses.

The first lady’s appeal is broad and deep among Democrats and independents, and she is particularly strong among black voters. Recent polls place her among the most favorably viewed figures in politics today; an August Gallup poll had nearly two-thirds of voters' saying they had a positive impression of her.

Clinton is already getting the support of 9 in 10 black voters, according to the latest ABC News/Washington Post poll. But President Barack Obama got an even larger share.

The Clinton campaign hopes Michelle Obama drives up interest among those who were more enthusiastic to cast ballots for her husband than they are to vote for Clinton.

“Let’s face it, elections aren’t about who votes. It’s about who doesn’t vote,” Michelle Obama said at a campaign event today in Philadelphia.

Then there’s Sanders, who did real damage to Clinton, particularly among independents, over the long primary battle few thought he would endure. New Hampshire was his breakthrough state against Clinton, and that’s where he campaigned with her this afternoon.

Despite the fact that he was never a Democrat before running for president, Sanders has been embraced by the party's base. One poll put his favorability rating among Democrats at 67 percent right after the Democratic National Convention, where his supporters were famously loud in wishing he had been the nominee instead of Clinton.

Michelle Obama and Sanders were political opponents of Clinton’s before this campaign.

Now they line up alongside a Murderers’ Row of surrogates — a sitting president, a former president, a sitting vice president and other luminaries such as Sen. Elizabeth Warren of Massachusetts — in fanning out for a candidate who needs specific help.

ABC News’ Adam Kelsey and Ryan Struyk contributed to this report.