Donald Trump speaks at a campaign event at Trump Doral golf course in Miami.

Donald Trump speaks at a campaign event at Trump Doral golf course in Miami. Carlo Allegri/Reuters

Businessman Donald Trump officially became the Republican nominee at the party’s convention in Cleveland.

What Donald Trump is doing on the campaign trail

What Donald Trump is doing on the campaign trail

As rosy exit polls began coming in from Indiana on Tuesday night, Donald Trump turned his attention to the next phase of his run for the White House — and his next opponent, Hillary Clinton.

The general election, he suggested in an interview, will not find him dialing back his scorched-earth approach to winning.

“Her past is really the thing, rather than what she plans to do in the future,” Trump said. “Her past has a lot of problems, to put it bluntly.”

Through this wild GOP presidential primary race, Trump has dispatched his opponents with insults, slurs and scornful nicknames.

“I haven’t devoted any time, effort, energy to Hillary yet. I haven’t started on that process because I’ve been focused on the nomination, which is probably wise,” he said. “With Hillary, I will be starting the process as soon as this is over.”

Republican presidential candidate Donald Trump held a campaign event at Trump Tower in Manhattan, after sweeping the Indiana primary. (Victoria Walker/The Washington Post)

He will be up against a different kind of challenge: a battle-tested adversary — and a general-election electorate that is broader and more diverse than the voters who have dominated the Republican primaries and caucuses.

[The question of the moment: What would Trump be like as GOP nominee?]

“What happened on the other side is instructive, but what you’ve seen there is a lot of folks on that side let his attacks go unanswered,” said Joel Benenson, Clinton’s pollster and chief strategist. “What happens going forward, I think you’ll see, is that when he does this, we’ll be aggressive.”

Republican contenders were constrained in attacking the front-runner by their fears of alienating Trump’s passionate supporters, while Democrats say they will have no such qualms in taking him on.

Clinton, moreover, is a known figure to voters — for better or worse — by virtue of having been on the national stage for nearly a quarter-century as a first lady, senator, presidential contender and secretary of state.

“She’s been the target of sexist vitriol and hate for the better part of three decades. She’s not only survived that but thrived. She certainly can withstand Trump’s name-calling,” said David Brock, who once was part of the anti-Clinton scandal machine and has since helped found several major outside groups that do battle on her behalf.

Yet those battles have also taken a toll. Polls consistently show that voters have misgivings about her character. In a Washington Post-ABC News survey in early March, only 37 percent of respondents said they found Clinton honest and trustworthy, while 59 percent said they did not.

After losing the Republican primary in Indiana, Sen. Ted Cruz (R-Tex.) said he was "leaving it all on the field." GOP front-runner Donald Trump commended Cruz, calling him "a tough, smart competitor" - a complete reversal from the insults he had been using earlier in the day. (Sarah Parnass/The Washington Post)

Meanwhile, there is an ongoing Justice Department investigation into whether her use of a private email server while she was secretary of state compromised national security.

But Clinton will have the benefit of a massive, well-financed net of protectors and defenders.

“The best defense against someone like Trump is a good offense, as long as it is the right offense,” said Geoff Garin, who was a top official in Clinton’s 2008 presidential campaign and now works with a pro-Clinton super PAC. “We at Priorities USA are ready to have Hillary’s back and keep a spotlight focused on the things that lead voters to conclude he would be a bad choice and a risky choice as president.”

In the Republican primary contest, Trump delighted in coming up with lethal labels for his opponents: “Low-energy” Jeb Bush, “Little Marco” Rubio, “Lyin’ Ted” Cruz.

He has already started road-testing labels for Clinton.

“She doesn’t have strength or stamina,” he has said of a woman who has boasted of logging nearly 1 million miles in her four years as the nation’s chief diplomat. In recent weeks, Trump has referred to her as “Incompetent Hillary.” His latest favorite is “Crooked Hillary.”

On Monday, the day before Indiana’s primary, Trump had lunch in an Indianapolis deli with Edward Klein, the author of several sensational anti-Clinton books that have been largely discredited.

[Indiana primary election results]

Clinton’s defenders are sure to dismiss Trump’s efforts to dredge up both facts and innuendo about her past as old news.

But her longtime critics say Trump can find a fresh audience for them.

“She’s never been the nominee. Even though in the ’90s, ‘Crooked Hillary’ was a known commodity as first lady, there’s a difference between that and being the nominee for president of the United States,” said David Bossie, a longtime Clinton foe and occasional Trump adviser who heads the conservative group Citizens United. “Donald Trump, I believe, thinks that his path to victory is to make every voter in America think of ‘Crooked Hillary’ as they go to the ballot box.”

Then again, Trump’s own negatives are even higher — and in fact would make him the least popular major-party nominee in modern history.

“There are not enough white men to elect Trump president, and he has seriously alienated voters of color, college-educated white women and younger voters,” Garin said. “The same shoot-from-the-lip outspokenness that many Republican primary voters found appealing about Trump makes general-election swing voters think he would be a huge risk in the Oval Office.”

And that is before Clinton and the organizations that support her begin spending in earnest against him.

“He’s about to walk into a $1 billion buzz saw,” said Stuart Stevens, a top strategist for 2012 GOP nominee Mitt Romney and a persistent Trump critic.

And some of the fodder will be coming from Trump’s own party. At a news conference Tuesday morning, hours before he dropped out of the GOP race, Sen. Ted Cruz (Tex.) unloaded on the front-runner, calling him a “pathological liar,” “utterly amoral” and “a narcissist at a level I don’t think this country’s ever seen.”

That footage is all but certain to show up again in Democratic ads.

Clinton strategist Benenson said Trump should be more concerned with raising his own image rather than scuffing up the presumptive Democratic nominee’s.

Moving toward a general election, he said, “you’re now not talking to a subset of one party in America. You’re talking to Democrats, independents, Republicans.”