Elsewhere, Cruz is already outmuscling Trump in precinct and county-level meetings being held in states that won't finalize their delegations until late next month.
As the maneuvering continues, Trump and his lieutenants continued arguing that the entire delegate selection system is "rigged" and designed to rob a party outsider of his earned support.
"What this election has shown is that when voters participate, Donald Trump wins. When the bosses participate, Donald Trump's interests are not there because he's the outsider," senior aide Paul Manafort told ABC's "This Week."
Manafort said that his campaign will be formally protesting the way delegates were chosen in Missouri, Colorado and elsewhere, but he declined to specify where and why exactly such challenges will be made.
Here's a look at some of what's transpired in recent days:
FLORIDA: 99 delegates
"The [party] bosses are picking the delegates, and it’s a very bad thing," Trump charged over the weekend.
Perhaps nowhere is that more accurate than in Florida. State party rules allow 81 of the state's 99 GOP delegates to be chosen by county party officials. If a congressional district overlaps multiple counties, the top three party leaders in each of those counties get together to pick a slate.
It happened over the weekend, when party leaders gathered behind closed doors — no public audience, no news media — to pick among applicants. In Miami-Dade County, selections were made at a cigar factory. In the Tampa area, Republican leaders gathered in an office park by an airport.
In three Tampa-area congressional districts, party leaders installed themselves or local lawmakers. In Miami, the slate included the chairman of the Miami-Dade GOP, a close friend and former aide to Sen. Marco Rubio (R-Fla.), while Trump supporters gathered outside to protest.
Nelson Diaz, who chairs the county party, dismissed the protests of Trump supporters.
"This is how it’s always been done" by Republicans across the state, he said.
Interest in the process is higher than ever before. Normally 10 to 15 people show up interested in serving as a national convention delegate. This year, Diaz said about 30 people applied for seats from each of the congressional districts representing Miami.
But Diaz was one of the people chosen to represent his Miami-area district.
"I spend a lot of time working for the party, more than the grassroots people, so what’s to say that a party leader doesn’t deserve or doesn’t have the right to go as a delegate?" he said.
When the Trump campaign says they're going to challenge the selection of delegates, it's likely they'll focus especially on the Sunshine State, where Trump won by double digits last month.
GEORGIA: 76 delegates
Cruz did well in a state Trump won handily as the Peach State's 14 congressional districts held conventions over the weekend.
In most districts, there’s a 2-to-1 allocation to the winner and runner-up for the first round of convention balloting. But in district after district, Cruz supporters won slots. In the 1st District, Cruz supporters won all three slots — including an 18-year-old high school senior and Cruz's Georgia grassroots director. In the 3rd District, two local Cruz organizers won seats — even though Trump's team would argue they were entitled to two.
In the 10th District, Bill Cowsert, the Georgia Senate majority leader, won a delegate slot — even though he supports Ohio Gov. John Kasich, who didn't perform well in the state. In the 11th District, former U.S. representative Bob Barr and Scott Johnson, Cruz's Georgia director, also won seats.
Trump's Georgia director, Brandon Phillips, won a seat in the 2nd District. But there was little organization by the Trump campaign elsewhere in the state.
INDIANA: 57 delegates
The state doesn't hold its primary until next month, but the Hoosier State GOP finalized its delegation last week behind closed doors. Many of the names on the list are supporters of Cruz and Kasich.
To be sure, the slate also includes Trump's Indiana director Rex Early. But here again, it appears that the Trump campaign was outmaneuvered. Kasich touted the results over the weekend, suggesting that a plurality of the delegation supports him.
KANSAS: 40 delegates
Cruz easily won the state's March caucus. On Saturday, Republicans in the 1st Congressional District picked two delegates for Cruz and one for Trump. The two Cruz delegates include state Sen. Tom Arpke, a co-chairman of the senator's campaign.
The state's three other congressional delegations picked their slates last month. The state will finalize its delegation at a state convention in mid-May.
OKLAHOMA: 43 delegates
There's less drama in Oklahoma because each of the state's congressional districts is required to pick one delegate each for Trump, Cruz and Rubio. Local party officials contacted over the weekend declined to release the names of their delegates, saying they were told not to do so by state party officials.
SOUTH CAROLINA: 50 delegates
The 1st Congressional District, encompassing Charleston, elected an entire pro-Cruz slate, despite Trump's commanding win in the state. Former state senator Mike Rose, a Cruz supporter, took the top spot and will serve with K.C. Lombard and Paige Duffy Lewis, who also support Cruz.
Lombard showed up for Saturday's meetings dressed in a Cruz jersey, according to the Charleston, S.C., Post and Courier.
VIRGINIA: 49 delegates
The 10th Congressional District — the only one that Rubio won in the commonwealth — elected a pro-Cruz slate of delegates. The Trump and Cruz camps ran slates wooing former Rubio supporters disappointed with the remaining choices.
Ultimately, state Sen. Richard H. Black, a Cruz supporter, won a top slot. He marveled at the turnout for the two most conservative candidates in a district that supported the more mainstream Rubio.
"If there’s anyone that the RNC would like to see lose, it would be Ted Cruz or Donald Trump,” Black told The Washington Post's Antonio Olivo. “I’m sure there are members of the establishment that would want something to happen to either one of these candidates along the way.”
WISCONSIN: 42 delegates
Cruz won here, depriving Trump of a critical April victory.
The state's full slate of delegates isn't scheduled to be released until later Monday. But the Badger State will be less dramatic than most because delegates are bound to Cruz until he releases them, if ever, or if Cruz drops below a certain threshold at the convention.
WYOMING: 26 delegates
Cruz won the 14 delegates up for grabs on Saturday in a state convention. As one of six states and territories that opted not to hold a caucus or primary, Wyoming Republicans gathered over the weekend after holding a series of little-hyped local conventions. That allowed Cruz supporters to win places at the state convention and then show up to elect other Cruz supporters to serve as national delegates. Cruz had already won nine national delegates during the state's county conventions.
In Wyoming, Trump’s local operation was clearly outmatched. Our Principles PAC, the best-funded anti-Trump group, piled a table with more anti-Trump brochures than there were voters who could read them. As The Post's David Weigel reported from the convention, Republicans could be heard grousing that the “fake” Trump literature was more plentiful than the actual Trump merchandise sitting near Cruz’s hospitality suite.
"We didn't even play there because it was a closed system and we didn't want to waste our money dealing with party bosses," Manafort told ABC about the Wyoming contest.
As if all of this wasn't enough, there's word that things could look bad for Trump next month in Nebraska, where Cruz supporters packed the early stages of the delegate-selection process held at the county level. Trump and Cruz are both competitive in the state.
The same thing is happening in Washington state, where Republicans don't vote until next month. Already Cruz is out-organizing Trump and Kasich at recent county and legislative-district meetings that elected 1,500 delegates to the state GOP convention. This means that the state GOP convention in Pasco, Wash., on May 18 is poised to be filled with Cruz supporters — regardless of whether he wins the primary.