On the night of Florida’s primary last week, Democratic front-runner Hillary Clinton speaks to a cheering crowd of supporters at her victory party in West Palm Beach, Fla. (Melina Mara/The Washington Post)

Democratic front-runner Hillary Clinton and her allies have begun preparing a playbook to defeat Donald Trump in a general-election matchup that will attempt to do what his Republican opponents couldn’t: show that his business dealings and impolitic statements make him unfit to be commander in chief.

Both the Clinton campaign and outside supporters are confident that she and Trump will almost certainly face each other in the general election and that the focus is shifting past her hard-fought primary campaign against Sen. Bernie Sanders of Vermont.

They are now focused intently on researching the billionaire real estate mogul’s business record, dissecting his economic policies and compiling a long history of controversial pronouncements that have captivated and repelled the nation in this tumultuous election season.

Neither the Clinton campaign nor several independent super PACs working on her behalf plan to respond with the same brass-knuckles style that Trump has taken with his Republican opponents, aides and outside supporters said. But in their view, Trump isn’t Teflon: Republicans waited too long to go after him, and they went about it the wrong way.

“What the Republicans did was too little, too late,” said David Brock, who runs two pro-Clinton super PACs now engaged in researching and responding to Trump. “It was petty insults. It was not strategic.”

Democratic front-runner Hillary Clinton said March 21 that the outcome of American elections in November 2016 will affect the U.S. relationship with Israel, emphasizing that "Israel's security is non-negotiable." (Reuters)

Justin Barasky, spokesman for the large pro-Clinton super PAC Priorities USA, said Republican candidates committed “malpractice” by failing to raise liabilities from Trump’s past or aggressively challenge him on offensive or incorrect statements.

Implicit in the effort is real worry about Trump’s outsider appeal in a year dominated by ­working-class anger and economic anxiety. The prospect that Trump could compete for some of the blue-collar voters who have flocked to Sanders, for instance — or to reorder the map of competitive states to include trade-affected Michigan or Pennsylvania — has prompted Clinton’s allies to leave nothing to chance.

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Yet, they also believe that, although Trump has motivated a loyal plurality of supporters in primary contests, he has limited ability to expand that support once the Republican field clears. Because of the litany of controversial pronouncements he has made, they expect a Trump nomination to make it easier to rally women, Latino and African American voters to turn out for Clinton. In fact, her aides are planning for a historic gender gap between Clinton and Trump.

Given Trump’s willingness to attack his opponents — and his pivot to going after Clinton in recent days — one clear presumption has emerged about the fall contest: It will be ugly.

That’s one reason the former secretary of state plans to counter Trump with high-road substance, policy and issues, according to one senior campaign aide. The idea is to showcase what Clinton’s backers see as her readiness for the job without lowering her to what they describe as Trump’s gutter.

The aide said the campaign’s day-to-day decision-making remains focused on Sanders. But Clinton swept all five states that voted Tuesday, and Trump did well, meaning both are far closer than any competitor to securing their respective party’s nomination. Clinton is also far ahead in polling in Arizona, a large contest this week, while Sanders is expected to pick up victories in other Western states that the Clinton campaign maintains will have little effect on her lead.

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A central lesson of Trump’s primary battle, the campaign aide said, is that he cannot be ignored — but also that he cannot be beaten at his own game. The key will be to maintain stature by focusing on her message of political unity and economic growth and by showing knowledge and strength on foreign issues. The aide spoke on the condition of anonymity to speak candidly about internal strategy.

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“It’s kind of mutually assured destruction: Both sides line up their nukes. It’s going to be just ugly and nasty and icky,” said another Democrat with longtime ties to the Clinton family. “The winner will not be the least bad of the two. The winner will be the one in the contest of that mutually assured destruction who also has a vision and a message about the future that is both inspiring and credible for the rest of the country.”

At the same time, her infrastructure of outside supporters will be poised to respond to what they expect will be Trump’s all-out war against Clinton on everything, both personal and political. Clinton’s backers acknowledged that she is also a divisive figure and that controversies such as her use of a private email server while secretary of state will not evaporate during the general election.

“We will not make the same mistake the Republicans made” by letting attacks go unchallenged, Brock said.

Trump has repeatedly brushed off polling indicating that he would lose in a head-to-head contest with Clinton. But after his victories in Florida and elsewhere last week, he sounded like a ­general-election candidate who recognizes the challenge ahead.

“We have to bring our party together,” he said. “We have something that actually makes the Republican Party probably the biggest political story in the world.”

Trump has benefited in the primary season from the failure of Republicans to unite behind a single foil to his candidacy — and from his own strategy of picking off successive targets whom he viewed as weak. Former Florida governor Jeb Bush and retired neurosurgeon Ben Carson both made the mistake, Clinton supporters said, of trying to ignore Trump’s insults or wait out a Trump decline that never came. Sen. Marco Rubio (R-Fla.) made the other mistake of trying to use Trump’s own tactics.

“You can’t beat him by being him,” Barasky said.

In a one-on-one race against Clinton, Trump would have less room to parry or pivot the same way, the senior Clinton campaign aide said, because Trump would have one target and one target only.

Barasky and others also predicted that Trump will emerge more damaged by his primary fight than Clinton, because of the deep divisions he has caused and exploited. Sanders supporters may not like Clinton, but their distaste for her doesn’t approach the antipathy or angst that many Republican voters harbor about Trump, they said.

Trump satisfied his loyal supporters by playing a character — the bully, the iconoclast — but he turned off many in his own party in the process, said several Clinton supporters who are studying the Republican race.

In fact, they believe Trump’s own words will make one of their central objectives easy: tearing him down in the eyes of women, notably Republicans and independents.

Several outside groups — including Emily’s List, which supports Democratic women who favor abortion rights — are compiling dossiers of statements denigrating women that were taken from the candidate’s own mouth, not just in this campaign but far into his past.

“You’re a mom and you’ve got your kids sitting on the couch and you watch the nightly news and you’ve got this guy saying things as a presidential candidate that you tell your kids not to say,” said Stephanie Schriock, president of Emily’s List. “You don’t call women bimbos; you don’t say that they’re fat.”

Women, including independents who sometimes vote Republican, are going to be repulsed, Schriock said.

Trump will also be a rallying point for Clinton’s message to black voters, particularly older ones, who view Trump’s rhetoric and his raucous rallies as reminiscent of the worst of America’s past.

At an MSNBC forum Monday, Clinton said that Trump’s rallies and his exhortations to violence resemble the “lynch mobs” of the South during the Jim Crow era. The remark came after videos from a Trump rally in Fayetteville, N.C., were widely disseminated and showed a white Trump supporter punching a black protester in the face.

“The secretary has hit on a really important chord that is running through the African American community: This community is 50 years or less from the civil rights images of dogs and hoses and frightening images,” said Rep. Sheila Jackson Lee (D-Tex.), who has endorsed Clinton. “That visual of the sucker punch is going to be ingrained in us forever. You can’t take it back.”

Several pro-Clinton super PACs are compiling research on Trump from his long career in business and much shorter career in politics. The strategy is still a work in progress, and ongoing research through polling, focus groups and forensic accounting, among other tools, will continue through the spring.

Much of the work is to search for vulnerabilities that in other years, with other candidates, would have already been exploited by other Republican candidates during the primary.

Plans are well underway to present Trump’s bankruptcies and management history to voters — particularly to women and the working class.

In addition, Trump opposes an increase in the minimum wage and has proposed tax breaks for the wealthy, positions that his Republican opponents could not go after but which Clinton supporters believe will play poorly in the general election.

People who suffered from Trump’s business decisions will be featured in testimonial advertisements and media campaigns, Brock said. The media strategy is not unlike several successful efforts in 2012 to tie Republican Mitt Romney to the layoffs and business closures that his company, Bain Capital, was responsible for.

“You’re definitely going to hear from a number of people who are former customers, clients, employees, who got the short end of the stick in various ways dealing with Trump,” Brock said. “That’s fertile ground.”

Schriock also noted: “It’s about character. It all ties to what kind of character does this man have.”

And it is about money. As the general election approaches, Clinton’s allies are preparing to draw from the discontent in Republican ranks to fill her campaign coffers.

“I’ve gotten phone calls and emails from a few major Republican donors who have said, in effect, ‘I will let you know when I’m ready to have you make an introduction for me,’ ” said Andy Spahn, president of a Los Angeles consulting firm and a longtime Clinton adviser and top Democratic fundraiser. “There is certainly an element of the Republican Party, be it voters or high-net-worth donors, who are uncomfortable with what is happening.”

Other Democrats also assessed that, in addition to GOP donors, Republican congressional candidates will run away from Trump in the general election, underscoring what they see as his thin qualifications — and the danger he poses to their own political fortunes.