Susan Page

USA TODAY

The Republican nomination is his. Now there's a new question: Can Donald Trump win the White House?

With a decisive victory in the Indiana primary Tuesday, the billionaire businessman who was initially ridiculed as a reality-TV candidate was declared the presumptive nominee by Republican National Chairman Committee Reince Priebus. Trump's final two rivals, Texas Sen. Ted Cruz and Ohio Gov. John Kasich, called it quits, sealing the most remarkable political rise in modern American history.

Now some of his primary rivals and other senior Republicans argue that Trump's lack of governmental experience and his unprecedented negative ratings — including among such crucial electoral groups as women, Latinos and young people — will doom his prospects in November. But as Trump likes to remind people, the conventional wisdom has been wrong about him from the start.

"It's been some unbelievable day and evening and year," Trump declared in a victory speech Tuesday night in the lobby of Trump Tower in New York, where he had announced his candidacy almost a year ago. “We’re going to win big league, believe me."

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He faces what could charitably be described as an uphill battle. A national CNN/ORC poll, taken April 28-May 1, showed Clinton with a daunting lead over Trump of 54%-41%. To win the White House, he needs to hold all of the states Mitt Romney won in 2012, with a total of 206 electoral votes, then add at least 64 more to get to the 270 mark to claim the presidency.

A look at five states that could hold the key to both how a Trump victory is possible and how difficult it will be. Here's one scenario that would give Trump 273 electoral votes — and the White House.

1. Hold Arizona: 11 electoral votes

In the past 16 presidential elections, Arizona has voted Democratic just once, in 1996. But Trump's characterization of Mexican immigrants as rapists and murderers and his vow to build a wall along the Southern border have energized Latino voters here. In the latest RealClearPolitics average of recent statewide polls, Clinton leads the state by 3.5 percentage points. She and Trump showed strength in Arizona in its primaries last month, each winning by double digits.

2. Hold North Carolina: 15 electoral votes

Democrats say North Carolina has been moving in the party's direction, but after Barack Obama carried the state in 2008 he lost it in 2012. Now Clinton leads Trump by 2 points in statewide polls, and both husband Bill Clinton and daughter Chelsea Clinton have visited the state in recent weeks. Boosted by her solid support among African Americans, Clinton won the primary over Vermont Sen. Bernie Sanders by 14 points in March; Trump edged Texas Sen. Ted Cruz by 3 points.

3. Flip Florida: 29 electoral votes

Florida defines a swing state: In the last six elections, Democrats have carried it three times, Republicans have carried it three times. In statewide polls, Clinton now leads, but by just 2.2 points. She's already returned to the state for campaign-related events since the Democratic primary in March, which she won by more than 30 points. But Trump has roots in Florida, including his lavish Mar-a-Lago estate in Palm Beach. He crushed Florida Sen. Marco Rubio in the primary by close to 20 points after pushing former governor Jeb Bush out of the race entirely. Would "Little Marco," as Trump called Rubio, pitch in to help in the fall?

4. Flip Ohio: 18 electoral votes

No Republican has won the White House without carrying Ohio, and since 1960 the Buckeye State has had a perfect record of going with the national winner. At the moment, Clinton holds a lead in statewide polls, but it's narrow: 3.5 points. In March, she easily won the state's Democratic primary. Trump lost the Republican primary to the home-state governor, John Kasich. But Ohio's struggling manufacturing base and its hard-pressed blue-collar voters could provide a receptive audience for Trump's message in the general election. Kasich would be in a position to boost the GOP nominee, if he chose to do so. And where was Clinton campaigning Tuesday? Ohio.

5. Flip Pennsylvania: 20 electoral votes

Pennsylvania hasn't voted Republican in the presidential race since 1988, but the state includes many of the white working-class voters who are Trump's most fervent supporters. In last week's primary, Trump won two-thirds of Republican voters who didn't have a college degree, defeating Cruz overall by more than 2-1. Clinton won the Democratic primary by 12 points. In statewide polls now, Clinton leads by 7.4 points. As in Florida and Ohio, Pennsylvania has a competitive Senate race that could also play a role.