Donald Trump and other top Republicans say they want the national convention that starts Monday to be a unifying moment to bring together a divided party and defeat Democratic rival Hillary Clinton.

Trump became the party's presumpitve presidential nominee in a stunning primary contest in which he defeated 16 major challengers with a message that appealed to millions of Americans disaffected by few economic opportunities, career politicians and a growing concern about national security.

“Trump isn’t part of Washington, and we’re going to be talking about he’s not part of Washington,” campaign manager Paul Manafort told “Fox News Sunday" about the convention. “He’s going to make a difference because he’s going to bring focus, purpose and change to Washington.”

However, Trump, a first-time candidate, and his insurgent campaign has alienated many Washington Republicans and donors whom he will need to defeat Clinton, in large part as a result of his comments about women, Muslims and Mexicans.

Such comments have resulted in a roller-coaster campaign that has at times appeared ready to go off the tracks. Still, Trump has continued to keep his likely general election race close with Clinton, the presumptive Democratic nominee.

A Washington Post/ABC poll released Sunday, the day before the start of the GOP convention in Cleveland, shows Clinton leading Trump 47-43 percent among registered voters, compared to the same poll showing her ahead last month by 12 percentage points.

Trump took a big step Friday in trying to bridge the gap with establishment Republicans in selecting Indiana Gov. Mike Pence as his running mate.

Pence, a former member of House Republican leadership with strong ties to top Republican donors, should help Trump better connect with social and fiscal conservatives and Capitol Hill leaders such as House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, who remain cautious supporters.

“I am here to introduce the man who will be my partner in the campaign and in the White House to fix the rigged system,” Trump said Saturday in officially introducing Pence as his running mate. “I found a leader who will help us deliver a safe society and a prosperous society.”

From the onset of their event Saturday, Pence made clear his willingness to go after Clinton, whose trustworthiness remains a concern among likely voters, particularly amid her email scandal as secretary of state.

“Americans can choose a leader who will fight to make America great again or we can elect someone who personifies failed establishment,” the 57-year-old Pence said. “Seven-and-a-half years of Obama and Hillary Clinton weakened the world."

He said Trump wants to cut taxes while Clinton plans to raise them and that Trump wants to repeal ObamaCare “lock, stock and barrel,” while Clinton is pushing a progressive agenda to expand government-backed, mandatory health insurance.

Party officials, with the backing of Republican National Committee Chairman Reince Priebus, appear to have squashed efforts to deny Trump the nomination by manipulating the rules for delegates awarded in the state primaries and caucuses.

Whether the so-called Never Trump movement makes a last-ditch effort before Trump makes his scheduled nominee acceptance speech remains unclear.

But Priebus told “Fox News Sunday” that convention security is in place and Trump’s acceptance speech Thursday will be a pivotal moment in the White House race.

“It's Thursday night, it's Donald Trump giving that speech, the balloons coming down and people saying I can see him in the White House,” Priebus told “Fox News Sunday.”

Priebus suggested Trump will be like Ronald Reagan in 1979, capable of delivering the kind of acceptance speech that took the steam out of Democratic rival Jimmy Carter’s campaign.

“I think we're in the same place,” he said.

Priebus also dismissed concerns about the convention being disorganized, in part because the final list of convention speakers has not been made public.  

“It’s not disorganized. It’s just different,” he told Fox.  “I can assure you that Donald Trump and his campaign can put on a show.”

Priebus said one of his biggest convention goals is to create more party unity -- considering Washington Republicans and other wings of the party have been slow to embrace Trump and his unconventional campaign.

“I want to show the unification process continuing and for me,” he said. “I'm serious. I think Thursday night is a really big deal for our party. Trump delivering that consistent, measured, pointed message -- the balloons drop, the band plays Donald Trump running for president in the White House, that's where we need to be.”

Trump said at a rally earlier this month in North Carolina: "We need unity in the Republican Party -- and I have to be honest, I think I can win without the unity, but we need it.”