TRENTON -- As the Republicans begin gathering in Cleveland this week in advance of their national convention, former Bogota Mayor Steve Lonegan and other opponents of businessman Donald Trump plan a last-ditch effort to deny him their party's presidential nomination.

They'll have as many as two shots at it, first the convention rules committee meeting beginning Thursday and then at the convention itself the following week. They are planning to lobby delegates in person and through an ad campaign.

"These delegates represent the entire Republican Party," said Lonegan, who led U.S. Sen. Ted Cruz's presidential campaign in New Jersey. "They have an obligation to pick the candidate to best beat Hillary Clinton. They have an obligation to the people to beat Hillary Clinton and carry the banner of the Republican Party and its principles. We think on both counts, Donald Trump does neither."

Trump will go into the convention with 1,542 delegates, well in excess of the 1,237 needed for the nomination, according to the Associated Press delegate count. Many of those delegates are party regulars who have no loyalty to Trump but support him under party rules requiring them to vote on the first ballot for the winner of their state primary.

The presumptive nominee is trying to prevent the challenge. A team of Trump supporters, including Republican National Committeeman Bill Palatucci, a top adviser to Gov. Chris Christie, is seeking to forestall efforts to change the rules.

Lonegan and other Trump opponents want to allow delegates to vote for whomever they choose. Their hope lives with convention rules committee members, who are chosen by the state parties, not the candidates. The rules committee will meet beginning Thursday.

Even if anti-Trump forces lose at the committee level, Republican lobbyist Jack Burkman, who runs another group opposing the presumptive nominee, said he expected the issue to be decided on the convention floor the following week.

"This is going to go to the floor," Burkman said. "I don't think they'll be able to stop that."

Their efforts could be bolstered by the 560 delegates pledged to Cruz, who unsuccessfully sought the GOP nominee and has yet to formally endorse Trump. Cruz has a majority of delegates in 10 states, according to a New York Times count.

Burkman, whose law firm was paid $1.4 million to lobby the federal government last year, said he expected the anti-Trump groups to coalesce once they get to Cleveland. Names being banded around as possible alternatives should they deny Trump the nomination include Wisconsin Gov. Scott Walker and former Massachusetts Gov. Mitt Romney, the 2012 GOP presidential nominee.

The outspoken Lonegan ran unsuccessfully for Senate against Democrat Cory Booker in the 2013 special election and lost to Christie in the 2009 Republican primary battle for governor. He is a former state director of Americans for Prosperity, the advocacy group backed by energy executive David Koch.

What unifies the opponents is the belief that Trump, who has praised the women's health-care provider Planned Parenthood, opposed cuts to Social Security, and contributed to Democratic candidates, is not a true conservative.

"Our people believe we are committing political suicide," Lonegan said. "I don't want to see the party commandeered by a candidate who two years ago was a Democrat who takes the party in whole different direction. We could set the conservative movement back for decades."

Burkman said Trump's conversion reminded him of conservative-turned-liberal activist Arianna Huffington.

"He's been for, he's been against," Burkman said. "I don't really know where Trump is."

While Lonegan is trying to build an organization to lobby delegates, Burkman is trying to fund anti-Trump efforts. He held a fundraiser at his Virginia home on Friday and set a goal of bringing in $1 million.

"We're sort of the electric power source," Burkman said. "Everything a presidential campaign needs money for, we need money for."

But state Sen. Michael Doherty (R-Warren), the most outspoken Trump supporter in the New Jersey Legislature, said he expects the anti-Tump movement to stall at the convention. And he scoffs at the notion that the real estate magnate isn't a conservative.

"For me, as a conservative, he's hitting all the buttons that conservatives care about," said Doherty, considered by many to be one of the most conservative members of the Legislature.

He also dismisses the argument that Trump can't beat Clinton.

"Anybody who says another candidate would be stronger is absurd," Doherty said. "Trump blew away the entire Republican field. Everyone of them."

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant. Find NJ.com Politics on Facebook.