Republican presidential candidate Marco Rubio campaigns in Atlanta, Georgia, on Monday. (Erik S. Lesser/European Pressphoto Agency)

In my school days, I read a poem called “If—” by the painfully dated Rudyard Kipling. He was a champion of imperialism, the white man’s burden and other such drivel, but the poem is a bully-pulpit exhortation to manliness that is not yet out of date. Its last verse begins “If you can talk with crowds and keep your virtue” and ends “you’ll be a Man, my son!” Marco Rubio ain’t there yet.

Instead, Rubio went into the sandbox with Donald Trump. Recently, he has suggested that Trump wet his pants. He’s pointed out that Trump uses some spray tan that gives him the hue of a just-wiped Wilson basketball and said (alleged?) that Trump has small hands. “And you know what they say about men with small hands,” he added. Then, after an unheard riff on the snare drum, he said, “You can’t trust them.” A relieved audience ventured a weak laugh.

Rubio’s challenge in this campaign was to show that he is not the callow youth he appears to be. He had to show he was bigger than the sum of his slight bio — a first-term senator whose only real accomplishment was to become a first-term senator. He had to show that Rick Santorum had merely frozen before the camera on “Morning Joe” when he endorsed Rubio and then could not come up with a single thing he had done in the Senate. If Rubio, as he himself says, is the candidate of the future, then so are his achievements.

Embedded in Rubio, along with a chip storing infinite sound bites, is one that glows red from ambition. (It’s a wonder he can get through airport security.) He runs for office when he can’t think of what else to do. Santorum, flustered by Joe Scarborough, neglected to mention Rubio’s true talent, which is the seduction of older and more powerful politicians. One such was Jeb Bush, who played Caesar to Rubio’s Brutus.

Rubio is remarkably conservative. He is opposed to same-sex marriage and the rest of the progressive social agenda, and he is so anti-abortion that he would not even countenance it in pregnancies caused by rape or incest. This puts him on the extreme of the anti-abortion movement, but as is often the case with Rubio, his inflexible rhetoric masks a flexible position. In a back-and-forth with Evan Osnos of the New Yorker about abortion, Rubio opened the door to “exceptions.”

Republican presidential candidate Marco Rubio took aim at Donald Trump Feb. 28, criticizing his rival's "small hands" and "spray tan." (Marco Rubio)

Rubio used to say that his parents were Cuban refugees. Not so. They were Cuban immigrants, having come to the United States two years before Fidel Castro took power. He was once one of the Gang of Eight in the Senate that wanted both to secure the border and to provide a path to citizenship for the country’s 11 million undocumented immigrants. He bailed, and reversed himself when things got hot. He now stands foursquare for whatever is popular.

The Rubio team is now saying its candidate had no choice — he had to get down in the mud with Trump or lose. This, with some variation, was the McCain refrain about Sarah Palin; she was supposed to be the game-changer. Instead, she fouled John McCain’s everlasting reputation. It is the same with Rubio. It is one thing to mock Trump’s ideas — to his face, preferably, in a debate — and quite another to make smirky remarks about the glow of his skin, the size of his hands or the capacity of his bladder. Rubio has more ambition than pride.

We live in Kardashian Country, I understand that. It is a place where Kim Kardashian rose to fame with a sex tape that’s available with the click of the mouse. (Standards have changed so fast and so radically that I fear the future, looking over my shoulder, wondering what kind of prig would write such a sentence.) Compared to this, Rubio’s infantile jabs at Trump are Gregorian chants. When it comes to decorum, it’s always Casual Friday in America.

Still, we are talking about the presidency. The president is both head of state and head of government — monarch and prime minister in one. He or she lives where Lincoln did, as well as TR and FDR, Jefferson and Reagan — to name just some — and makes decisions, sometimes, about who shall live and who shall die. This is a job for grown-ups — for people who embody the virtues Kipling set out in his poem.

It begins: “If you can keep your head when all about you are losing theirs . . .“

Marco Rubio has supplied his answer. He cannot.

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