Hillary Clinton spoke to supporters, Nov. 9, offering a message of thanks, apology and hope. Here are the key moments from that fervent address. (Sarah Parnass/The Washington Post)

Hillary Clinton spoke to supporters, Nov. 9, offering a message of thanks, apology and hope. Here are the key moments from that fervent address. (Sarah Parnass/The Washington Post)

Just days before the election, after weeks believing that Michigan was safely blue, the pro-Hillary Clinton super PAC Priorities USA polled voters there — only to discover that it was a one-point race.

The group quickly poured millions into the state. The Clinton campaign did similarly, and on the eve of the election, aides sent in Clinton herself, as well as her top surrogate, President Obama.

It was too late.

Clinton’s failure to attract enough supporters in Michigan and its Rust Belt neighbors Wisconsin and Pennsylvania cost her the election — and shocked the world. And while many reasons have been offered up, both inside and outside the campaign, one reality has emerged in the days since Clinton’s stunning loss, according to many Democrats interviewed for this article: a series of strategic mistakes, including some made in the final two weeks, probably sealed the deal.

One error was to stick with a long-standing, one-dimensional campaign strategy: attacking Donald Trump. That strategy had been devised despite overwhelming evidence, not only in Trump’s rise but also in Clinton’s struggles during the Democratic primary against Bernie Sanders, that the electorate was looking for political and economic change.

Another problem, some said, was to devote resources in states Clinton did not need to win — notably Arizona — instead of shoring up support in deep-blue states, notably the Rust Belt, that she did need.

“Why go to Arizona? Who the hell needs Arizona?” said Lou D’Allesandro, a state senator and Clinton supporter from New Hampshire, where Clinton appears to have narrowly prevailed Tuesday. “You go to Michigan. You go to Pennsylvania. You play to your strengths in this business.”

The lack of enthusiasm for Clinton among the Democratic voters who carried Obama to victory twice could not be overcome with a campaign message focused so heavily on Trump’s divisiveness, said David Axelrod, former chief strategist for Obama’s presidential campaigns.

“What you can’t do is you can’t manufacture enthusiasm,” Axelrod said. “There was an assumption that antipathy toward Trump would be enough to mobilize the base . . . a certain lethargy that sets in when you’ve had the White House for eight years. Your troops are just not as hungry.”

Axelrod added that “too much was assumed in the industrial Midwest.”

In the end, even as the campaign shifted resources and sent surrogates back into the Rust Belt, the message remained the same: Trump lacked the temperament to be president and was unfit for office.

To the bafflement of Democrats in Wisconsin, for instance, the late Clinton push there did not mirror the economic messaging of the local labor unions. One played back Trump’s worst remarks about women; another, his mocking of a reporter with a physical disability; the last, a warning from a nuclear technician who worried that a reckless President Trump would start a war.

That decision was backed by data showing that voters reacted most strongly to his controversial comments. But it did little to motivate Clinton’s base of supporters, especially when they were faced with questions about her judgment in using a private email server as secretary of state.

Again, in Wisconsin, the results proved the case — a state where Clinton did not make a single stop during the general election.

Clinton’s margin in Milwaukee, for instance, which boasts a heavily African American electorate that Democrats rely on to carry the state, far under­performed that of Obama in 2012. Trump, meanwhile, earned a similar vote count as 2012 Republican nominee Mitt Romney. He won the state not because he out­performed his predecessor but because Clinton under­performed hers.

“You can test a whole set of arguments against Donald Trump and always the top attacks on him had to do with temperament,” said Anna Greenberg, a Democratic pollster who worked on several down-ballot races in this cycle. “But you can have things that test well but don’t move people to vote.”

“Obviously we don’t know if it would have been different if she had a more consistent economic message,” Greenberg added, “but I think it’s hard to win without it.”

Clinton made a pledge to build “an economy that works for everyone, not just those at the top,” a mantra in nearly every speech while promising to be rebuild the middle class and create more pathways into it. She outlined myriad plans and proposals that she said would help deliver new jobs and rebuild U.S. manufacturing.

Yet, there was no simple or overarching message that tied it all together. As a rallying cry against economic injustice, a pledge to be “the small-business president,” for example, sounded bloodless.

Even among minority voters disinclined to vote for Trump, that message fell short.

“Pre-election research showed that among African Americans, their feelings of economic optimism were precipitously lower in this election than in 2012,” said Geoff Garin, a pollster for Priorities USA who conducted this research independently of the super PAC. “And their feeling that Clinton’s economic policies would help people like them were substantially lower.

“Those kinds of things affect people’s willingness to come out to vote.”

Some Democrats inside and outside of the campaign say that there is little Clinton could have done to stop the slide even if she had spent more time campaigning in Wisconsin and Michigan. The forces­ that caused her loss in the upper Midwest were also at work in places­ where her campaign sent her far more often and invested huge amounts of money, including Pennsylvania, North Carolina and Florida.

In some instances, there were factors in play beyond the control of the campaign. When the decision was made to send Obama to Michigan on the eve of the election, Democrats there counseled to send him to Detroit, where enthusiasm among the party’s African American base was sagging. But a funeral scheduled on Monday for a police office killed in a hit-and-run made that logistically messy, so Obama went to Ann Arbor instead.

By the time the campaign realized Clinton was in trouble there, it was too late. In the end, although Clinton won Detroit’s Wayne County in a landslide, she underperformed Obama there by 78,000 votes — vastly more than her statewide losing margin of roughly 11,000.

In calls with surrogates and donors this week, top Clinton aides and Clinton herself focused instead on a letter to Congress from FBI Director James B. Comey 11 days before the election. In it, Comey said the bureau had found a new trove of emails from Clinton’s private server that warranted examination. In the end, Comey declared that the investigation into her use of the server while secretary of state would remain closed. According to the campaign, that was too little, too late.

“It affected us a couple of ways. First, it blocked out the sun. We really weren’t able to break through for a couple of days,” communications director Jennifer Palmieri said on one such call Friday.

And secondly, the issues stirred up distaste among some voters, she said. “It adds to people who had doubts about the ticket, or it certainly didn’t help.”

On Saturday, Clinton laid blame squarely at Comey’s feet. She told top donors in a farewell call that the first FBI letter reopening the email inquiry stopped her momentum — and the second one shutting it down again, something that should have been good news, served to energize Trump voters.

“There are lots of reasons why an election like this is not successful. But our analysis is that Jim Comey’s letter raising doubts that were groundless, baseless, proven to be, stopped our momentum,” Clinton said.

“Just as we were back up on the upward trajectory, the second letter from Comey essentially doing what we knew it would — saying there was no there there — was a real motivator” for angry or disappointed Trump voters to turn out, she said.

After Comey’s Oct. 28 announcement, Clinton’s standing with suburban, college-educated voters plummeted across the board, undermining the centerpiece of her electoral strategy.

Clinton’s aides also believe that the renewed attention to the email story helped dampen enthusiasm among her base voters.

Democrats have long complained that the campaign failed to address the email issue swiftly over a year ago, and those frustrations bubbled over after her loss Tuesday.

“She should’ve apologized for that earlier, and people would have understood,” D’Allesandro said. “We all make mistakes. That’s why pencils have erasers.”

Instead, he said, “the email situation kept coming up and coming up and coming up, and it came back up again at the last hour.”

The road for Clinton had always been difficult. She was historically disliked, outdone narrowly in that characteristic only by Trump. And in seeking the presidency, she was asking voters to sign off on a third Democratic term, a historically difficult task for any governing party.

It was “a very proficient campaign with a very freighted candidate,” Axelrod said. “Not a great candidate, and not a great candidate in a time of change.”

Clinton also spent time and re­sources over the summer urging Republicans to abandon Trump, but exit polls showed that 90 percent stuck with the party’s nominee.

“The general election turned into a battle of negatives,” said Jeff Weaver, Sanders’s campaign manager in the primary.

Weaver noted that more of Clinton’s television ads could have focused on proposals such as debt-free college that have great appeal to working-class voters.

“I felt that given the strength of many of her programs, the fact that those things weren’t getting sufficient attention were a problem,” Weaver said.

Exit polls and polling data conducted during the campaign found that voters were aware of and in some cases repulsed by Trump’s brashness, but it was not enough to compel them to vote against him.

“There are many millions of people who did not vote for Donald Trump because of the bigotry and hate that fueled his campaign rallies,” Sen. Elizabeth Warren (D-Mass.) said Thursday in a speech at the AFL-CIO. “They voted for him despite the hate. They voted for him out of frustration and anger — and also out of hope that he would bring change.”

Sanders said, “The simple truth is a lot of the Democratic base did not come out to vote,” noting that white working-class voters deserting the Democratic Party is a “humiliation” for the party.

Asked whether he could have beaten Trump, Sanders said: “I hesitate to be a Monday morning quarterback.”

But he added: “In my heart of hearts, I think there’s a good chance I could have defeated Trump, but who knows.”

This story has been updated.

Karen Tumulty and Sean Sullivan in Washington and David Weigel in Wisconsin contributed to this report.