As the Republican race moves to the crucial battlegrounds of Ohio and Florida among three other states on Tuesday, Tea Party support promises to help Trump's campaign offset its relative lack of on-the-ground organization compared to Texas Senator Cruz, his closest rival nationally.
Having loyal Tea Party supporters could also help him fend off moves to block his nomination at the Republican National Convention in July if he falls short of the threshold of 1,237 delegates that would guarantee him the party's candidacy.
A Reuters review of Trump's list of 66 Ohio delegates -- who would represent him at the nominating convention if he wins the primary and provide crucial support in the event of a contested convention -- found that 28 are Tea Party leaders, members or are otherwise linked to the movement, including officials who have been featured speakers at Tea Party events.
Using the same benchmark, 27 of Cruz's delegates have links with the grassroots group, which sprang to national prominence in 2009 on anger over government bailouts, and demands for tax cuts and less “intrusive” government.
Despite Trump's mixed record as a conservative, the real estate mogul’s promises to shake up Washington, throw out illegal immigrants and tear up "unfair" trade deals have won over many influential Tea Party followers, according to interviews with activists across more than a dozen states.
"Trump has never asked me for a dime and being self funded he's the only one that can blow up the Republican Party establishment," said Ralph King, a Trump delegate and member of the Cleveland Tea Party.
"If the primaries result in a contested convention, I'm in his corner all the way."
Recent polls have shown Trump performing well among voters who identified as Tea Party supporters.
A Feb. 29 CNN poll had 56 percent of Tea Partiers favoring Trump compared to 16 percent for Cruz. A March 9 Quinnipiac University poll had Trump leading Cruz 48 percent to 40 percent among Tea Party voters in Florida, while Cruz led Trump with 38 percent to Trump's 33 percent in Ohio.
"Trump has tapped into Tea Party emotions, gaining the support of many of the most hacked off and motivated voters out there," said Republican strategist Ford O'Connell. "It was a brilliant move."
The influence of the amorphous Tea Party has waned nationally, but it remains a potent force in many states through its thousands of committed grassroots activists.
For conservative purists, Cruz checks all the right ideological boxes of limited government and lower taxes.
Trump, on the other hand, says he would maintain government programs such as Social Security and has called for higher taxes on the most wealthy Americans. In 2008, he voiced support for the government's rescue package for major banks.
After Trump's strong showing in a string of states on "Super Tuesday" last month, Jenny Beth Martin -- co-founder of a national umbrella group called Tea Party Patriots - lambasted him as a conservative of convenience.
"Trump is about love of himself. But the Tea Party is about love of country and the love of our Constitution," she said at this month's Conservative Political Action Conference.
Ned Ryun, founder of American Majority, a group that trains conservative grassroots activists, said Trump's outsider persona is key to his appeal to Tea Party activists.
"Cruz people feel they can work within the status quo," said Ryun. "Trump people say screw the status quo, we're sick of it."
The billionaire has quietly maintained contacts with the movement since at least 2011, when he was flirting with a presidential run in the 2012 election.
More recently he has courted activists, focusing on prospective delegates. Trump broadened his appeal among Tea Party members in January when he secured the endorsement of former Alaska governor Sarah Palin, who commands strong loyalty among many in the movement.
At the South Carolina Tea Party convention in January 2015 in Myrtle Beach, Trump spent 45 minutes with eight Tea Party activists, test-marketing themes like immigration, according to attendees.
The effort brought converts. One of those present, Gerri McDaniel, ran Trump's grassroots efforts in South Carolina. Another, Jeanne Seaver, did the same in Georgia. He won both states' primaries.
Atlanta Tea Party co-founder Debbie Dooley also attended that meeting and aims to be a Trump delegate.
On the first ballot of the Republican convention in July she would be obliged to back him, but says she would continue to back him if voting goes to a second round when delegates become free to vote for whichever candidate they choose.
"I'll back Trump to hell and back," Dooley said.
In Michigan, New Hampshire and Nevada, Trump's successful efforts were helped by state directors formerly employed by Americans for Prosperity, a group backed by the billionaire Koch brothers that has courted Tea Party groups for years.
His Florida field director Ken Mayo held the same post at Americans for Prosperity.
Trump tapped a local Tea Party leader -- Rob Scott -- to run his campaign in Ohio. Of Trump's 21 delegates from New Hampshire -- the first primary he won -- 13 have Tea Party links or affiliations.
Delegate lists for Florida and Michigan -- another state that votes on Tuesday -- are not yet available because those states pick delegates at conventions after their primaries. In Ohio, candidates submit delegate lists in advance.
Trump still trails Cruz on get-out-the-vote efforts, strategists and activists say.
June Pitts, a Tea Party activist in Illinois, said in previous elections she has worked at campaign offices. But Trump doesn't have one in Chicago, so Pitts is making calls herself ahead of the state's March 15 vote.
In Tiffin, Ohio, Trump delegate Jim Green said he spent $700 of his own money on yard signs before the campaign began sending him paraphernalia for free.
Glenn Newman, a Trump delegate and activist in southeastern Ohio, has also been left to his own devices.
Trump's campaign "is being put together like a puppy chasing a pickup truck," Newman said. "They're just playing catch-up."