Flake opened his essay with an oblique shot at Trump, quoting him as he wrote: "Someone recently said, 'When Mexico sends its people, they're not sending their best.' The man who said that never met Manuel Chaidez.'"
Seizing on Trump's general assertion about Mexico, Flake wrote about his experience growing up with Chaidez, a young man who illegally immigrated to the US and worked on the family's ranch. Flake praised Chaidez's character and work ethic, and argued against Trump's proposal to reform the current immigration system
by reducing unskilled immigration and creating a merit-based system -- reforms that targets workers like Chaidez.
Flake wrote: "America would be a lesser country without Manuel Chaidez, and so many like him."
"His capacity for hard, backbreaking work was his sole credential in life. By no Washington bureaucrat's estimation would he have been judged a 'high-value immigrant.' He didn't speak much English. He didn't come from money. He hadn't finished high school. He had no technological innovation to his credit, nor had he started a business," Flake wrote. "In other words, count Manuel among the 99 percent of immigrants who have ever come to this country, including many of our ancestors, the 'wretched refuse' who got here as fast as they could and who made this country what it is once they arrived."
But, Flake continued, Chaidez's determination and grit set him apart.
"My dad would occasionally hire some of my high school buddies (to work on the family ranch). The work was so hard that they often washed out after a day or two. Not Manuel," Flake wrote. "Just as my family members bear the aches and pains of a lifetime of work on the F-Bar, so, too, does Manuel. All told, he devoted 24 years of his life to the ranch."
Flake's op-ed follows an intensification of his antagonistic relationship with Trump -- earlier this week, Trump took to Twitter to boost his 2018 primary opponent
, the latest episode in a long running feud between the two.
Flake recounted the crucial role Chaidez played on the family ranch, writing that "without such work there is no ranch. Without ranches, my town and towns like it falter. And so in my estimation, Manuel is just about the highest-value immigrant possible, and if we forget that, then we forget something elemental about America."
And the Arizona Republican -- who has emerged as one of the Republican Party's most vocal Trump critics -- closed his essay directly rebutting the President's proposal.
"When re-evaluating immigration policy, it is right to give priority, through a point system or otherwise, to those who have skills and abilities unique to the new economy. We did this in 2013, in the bipartisan immigration bill that passed the Senate. But there must always be a place in America for those whose only initial credentials are a strong back and an eagerness to use it."