The beginning of the end for Ted Cruz
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Sen. Ted CruzRafael (Ted) Edward CruzProtesters confront Cruz at airport over Kavanaugh vote O'Rourke targets Cruz with several attack ads a day after debate Election Countdown: O'Rourke goes on the attack | Takeaways from fiery second Texas Senate debate | Heitkamp apologizes for ad misidentifying abuse victims | Trump Jr. to rally for Manchin challenger | Rick Scott leaves trail to deal with hurricane damage MORE (Texas) has run a brilliant campaign, and if it were not for Donald TrumpDonald John TrumpTrump renews attacks against Tester over VA nominee on eve of Montana rally Trump submits 2017 federal income tax returns Corker: Trump administration 'clamped down' on Saudi intel, canceled briefing MORE, he'd probably be on the verge of wrapping up the Republican nomination by now. The Texas firebrand knew long before others that the party's primary schedule and delegate allocation rules played to his advantage, not to an establishment candidate like former Florida Gov. Jeb Bush. From his arrival in the Senate, Cruz has bent the political space-time continuum around himself by demonstrating GOP leaders' inability to govern effectively or deliver on their promises to conservatives.

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But he has made a fatal mistake. After excoriating the GOP establishment in the Senate and on the campaign trail, Cruz has now made common cause with the party in a desperate attempt to stop Trump. Wisconsin marked the turning point. Initially, he was coy about accepting the party's support. He did not court it, but Wisconsin was crucial to slowing Trump's momentum. And it worked. The Texan took 36 of the state's 42 delegates and appeared to have dealt a setback to the New York real estate mogul. But by cooperating with the party in Wisconsin, Cruz crucially altered the narrative of the campaign. The core of his electoral value proposition has been fierce opposition to the party's leaders. Once he tacitly accepted the party's embrace, he began to morph from a conservative stalwart to an opportunist.

The end of the beginning came in mid-March when establishmentarian Sen. Lindsey GrahamLindsey Olin GrahamGOP leaders hesitant to challenge Trump on Saudi Arabia Election Countdown: O'Rourke goes on the attack | Takeaways from fiery second Texas Senate debate | Heitkamp apologizes for ad misidentifying abuse victims | Trump Jr. to rally for Manchin challenger | Rick Scott leaves trail to deal with hurricane damage Five things to know about 'MBS,' Saudi Arabia's crown prince MORE (S.C.) endorsed Cruz. The beginning of the end came with Cruz's victory in Wisconsin on April 5, when the media portrayed it as a product of an unholy alliance between Cruz and the establishment. This narrative fed directly into discussions of scenarios in which Cruz would conduct raids on Trump's delegates. In turn, the party would make changes in the convention rules and use Trojan-horse delegates to hand the nomination to Cruz, or a white-knight candidate such as Speaker Paul RyanPaul Davis RyanGOP leaders hesitant to challenge Trump on Saudi Arabia Republicans should prepare for Nancy Pelosi to wield the gavel Ryan signals support for sanctions if Saudis killed Khashoggi MORE (Wis.). Cruz appeared too-clever-by-half, or worse, a patsy being played by the establishment to, first, turn away Trump, then deny the nomination to Cruz.

A kiss by the GOP establishment in 2016 has been the kiss of death. This has been the most consistent pattern of the campaign. Yet, as strategic as Cruz has been in his run, he seems to have missed this cautionary lesson. Or perhaps he believed he was immune, or he felt the opportunity slipping away and acted in desperation.

According to the RealClearPolitics average of national polls, Cruz hit his peak of the 2016 campaign on April 6, the day following the Wisconsin primary. After being stuck at 20 percent for two months, the Texas senator's support jumped 14 percentage points in 30 days, and he closed the gap with Trump to 7 points. The trend reversed when Cruz's Faustian bargain  became clear. He began to fade over the next 19 days and Trump's lead almost doubled.

The pattern is more evident in state polling. According to six polls conducted in New York between March 29 and April 7, Cruz's support stood at 19 percent around the time of the Wisconsin primary. By primary day, his share of the vote was less than 15 percent and he had lost by 46 points. In Maryland, an NBC/Marist College poll showed Cruz reaching his peak at 29 percent between April 5 and April 9 and closing the gap with Trump to 12 points. When the returns came in only 17 days later, Cruz had drawn less than 20 percent of the vote and lost by 36 points.

In Pennsylvania, two polls conducted between April 1 and April 7 showed Cruz with an average of 25 percent of the vote, 18 points down to Trump. When votes were counted, Cruz had won less than 22 percent of the vote and lost by 35 points. His support saw a similar dramatic collapse in Connecticut after the Wisconsin primary.

The pattern holds outside of the Northeastern states. A Field poll conducted in California between March 24 and April 4 showed Cruz's support at 32 percent, within 7 points of Trump. Three weeks later, a Fox News poll found the Texan's support had fallen to 22 percent and he was trailing Trump by 27 points.

All of these polls were conducted before Cruz and Ohio Gov. John Kasich reached their ill-fated agreement to avoid competing with each other in Indiana, Oregon and New Mexico. Not only did the agreement have a very short half-life, but it cemented impressions that Cruz would make any deal with the party establishment to remain viable. Now he has tapped former Hewlett-Packard CEO Carly Fiorina in an attempt to put California back in play, a curious move considering that Fiorina was trounced in her 2010 Senate race in the state, in a Republican year against an apparently vulnerable incumbent. The move has all the markings of desperation.

Diehl is a former chief of staff of the U.S. Treasury Department, director of the U.S. Mint and staff director of the Senate Finance Committee.