It took them nearly two months to do so, but John Kasich and Ted Cruz are finally taking Mitt Romney's advice.
When the 2012 Republican nominee lambasted front-runner Donald Trump in March, he called for a strategic effort to stop the New York businessman.
"I would vote for Marco Rubio in Florida, for John Kasich in Ohio, and for Ted Cruz or whichever one of the other two contenders has the best chance of beating Mr. Trump in a given state," Romney said during a speech delivered in Salt Lake City.
Now, with Trump fresh off a near sweep of New York's 95 delegates, and poised to possibly run the table in Tuesday's five primaries, Kasich and Cruz are trying to divide and, if not conquer, at least stop Trump from doing so.
Their two campaigns sent out near-simultaneous emails Sunday night announcing an unofficial detente: Kasich will stay out of Cruz's way in the upcoming Indiana primary, and Cruz will avoid campaigning in New Mexico and Oregon.
From Cruz's campaign manager, Jeff Roe:
"To ensure that we nominate a Republican who can unify the Republican Party and win in November, our campaign will focus its time and resources in Indiana and in turn clear the path for Gov. Kasich to compete in Oregon and New Mexico, and we would hope that allies of both campaigns would follow our lead."
And from the head of Kasich's campaign, John Weaver:
"Our goal is to have an open convention in Cleveland, keeping Trump from winning a plurality in Indiana is critical to keeping him under 1,237 bound delegates before Cleveland."
The idea is to stop splitting up the "anti-Trump vote" and keep their mutual opponent from earning the 1,237 delegates he needs to avoid the contested convention that is both Kasich's and Cruz's only hopes of winning the GOP nomination.
It's a last-ditch effort, for sure. And it has one prominent Kasich supporter scratching his head.
"I support John, but I don't agree with this strategy," former Pennsylvania Gov. Tom Ridge told NPR's Morning Edition. "I'd rather have John talking about why he would be the best nominee. ... I'd prefer him promoting John rather than stopping Donald."
Furthermore, the two-term Republican governor said, "It plays into Trump's narrative. He keeps whining about the primary. When he wins, it's fine; when he doesn't, it's rigged. But the fact of the matter is, the narrative says, 'They're trying to gang up on me,' and it reflects that."
Indeed, hours after the Kasich and Cruz campaigns made their not-quite-but-kind-of joint announcement about their nonaggression pact, Trump released a statement saying, "Collusion is often illegal in many other industries and yet these two Washington insiders have had to revert to collusion in order to stay alive."
"Because of me, everyone now sees that the Republican primary system is totally rigged. When two candidates who have no path to victory get together to stop a candidate who is expanding the party by millions of voters (all of whom will drop out if I am not in the race) it is yet another example of everything that is wrong in Washington and our political system."
Trump picked up on that Monday, mocking Cruz as a whiny baby and making fun of the way Kasich eats.
Trump has been hammering home his complaints about a "rigged" primary system in campaign appearance after campaign appearance in recent weeks, as Cruz and Kasich have talked more openly about winning the nomination by persuading convention delegates to shift their allegiances during multiple rounds of floor balloting.
The rhetoric picked up during a stretch where Cruz outmaneuvered Trump in statewide delegate conventions in Colorado and other states.
Trump's pre-emptive push may be working: In a recent poll conducted by NBC News and the Wall Street Journal, more than 60 percent of Republican respondents said the candidate with the most delegates going into Cleveland should be given the nomination, regardless of whether it's a majority.
In his Sunday-night statement, Trump called Kasich and Cruz "mathematically dead." That's been true for Kasich for weeks — he has no way of winning the delegates he would need to take the nomination, unless the convention goes to multiple ballots and delegates begin changing their mind.
A clinched nomination has been a political — but not mathematical — long shot for Cruz for weeks, as well. If Pennsylvania, Maryland and other Northeast states go for Trump by wide margins Tuesday, Cruz will be mathematically eliminated from a first-ballot win.
In theory, the Kasich-Cruz collaboration could have an impact on next week's Indiana primary. Polls show a relatively close race in the 57-delegate state, with Trump holding single-digit leads over Cruz and Kasich.
Cruz is already focusing heavily on the state, holding far more events there than in the states voting this week. About half of Indiana's delegates will be awarded to the statewide winner. The rest will be divvied up by congressional district.
"There's some disappointment on behalf of Kasich supporters in Indiana, but they also understand the strategic decision," Kasich's Indiana campaign co-chair, Carmel Mayor Jim Brainard, said. "It's a recognition by both campaigns that the goal is to win in November."
Still, it's not clear how much influence the Cruz and Kasich pronouncements will carry.
On Monday, Cruz wasn't exactly gracious toward Kasich or showed any sign of collaboration. Instead, he boasted about it this way: "It is big news today that John Kasich has decided to pull out of Indiana to give us a head-to-head contest with Donald Trump."
And during a Philadelphia campaign stop, Kasich said he would still welcome support in Indiana.
"I've never told them not to vote for me," he said at a diner in Philadelphia. "They ought to vote for me."