Ted Cruz's conversion from a Trump foe to a Trump supporter detailed in new book

Sen. Ted Cruz (R-TX) is one of Donald Trump's strongest allies in Congress but, of course, that hasn't always been the case.

The Texas Republican had famously urged Republicans to "vote your conscience" at the 2016 GOP convention, but Cruz understood he had to make amends with the party's hardcore conservative base who loved the nominee who insulted his wife and accused his father of murdering John F. Kennedy, according to excerpts from a new book, "In Trump's Shadow," written by reporter David Drucker and republished by Fox News.

"Between Cruz and [close adviser Jason] Johnson, they both agreed that framing an endorsement around the critically important issue of the balance of power on the Supreme Court was the best approach," Drucker wrote. "After Associate Justice Antonin Scalia died in February 2016, Senate Majority Leader Mitch McConnell refused to give any nominee of Barack Obama's a hearing, saying it was an election year and that voters should decide which presidential candidate they preferred to have control of the appointment. With millions of Republican voters weighing the same decision, it seemed a plausible way for Cruz to explain his change of heart."

"Johnson offered Cruz one crucial piece of advice," Drucker added. "If Cruz was going to back Trump, he had to be willing to go all the way, no fancy language or rhetorical contraptions about the endorsement being about anything other than what it was about — supporting Trump 110 percent — or Cruz would never recover."

The senator had been deeply concerned about what a Trump presidency would look like, and had said so publicly, but he brushed aside those concerns and offered his full endorsement.

"Cruz and Trump would proceed to have a rather cordial and productive relationship," Drucker wrote. "They talked on the phone often, and Cruz now and again convinced Trump to make this or that policy decision. In 2018, when Cruz was in dire straits versus O'Rourke, Trump even traveled to Houston and put on one of his signature campaign rallies to boost the senator's reelection prospects."

"Of course, when Trump ran for reelection two years later and put on a pandemic-altered convention that featured televised coverage of dozens of prominent Republicans speaking on his behalf, Cruz wasn't invited," he added.