When a Vesuvius like John McCain tells you that you belch too much smoke and spew too much fire, you know you've got a problem.

And Ted Cruz, a Republican freshman in the Senate who has been front and center in his party's effort to squash Chuck Hagel's nomination as secretary of defense, has a problem. He's an ornery, swaggering piece of work. Just six weeks since his arrival on Capitol Hill, he's already known for his naysaying, his nit-picking and his itch to upbraid lawmakers who are vastly senior to him, who have sacrificed more than he has and who deserve a measure of respect, or at least an iota of courtesy. Courtesy isn't Cruz's metier. Grandstanding and browbeating are.

He sits on the Senate Armed Services Committee, and during its final meeting on Hagel's nomination, he made such nefarious and hectoring insinuations about Hagel's possible corruption by foreign influences that McCain, who'd gleefully raked Hagel over the coals himself, more or less told Cruz to cool it. It was an unforgettable moment, and one that Republicans shouldn't soon forget, because Cruz, 42, isn't simply the latest overeager beaver to start gnawing his way through the halls of Congress. He's a prime illustration of what plagues the Republican Party and holds it back.

A fascinating illustration, too. On the surface, he should be part of the solution: young, Latino, with a hardscrabble family story including his father's imprisonment in Cuba and escape to the United States. But Republicans who look to him and see any kind of savior overlook much of what drags the party down, which isn't merely or even principally the genealogy of their candidates. It's the intransigent social conservatism, the whiff of meanness and the showy eruptions. It's what Cruz, who rode a wave of Tea Party ardor to victory in Texas in November, distills.

Note in particular a Republican pollster's recent interviews with Ohio voters. When the pollster asks them to play word association with "Republican," the answers indeed include a few descriptions that the profiles of Florida Sen. Marco Rubio and Cruz push back against: "rich," "white." But the adjectives "rigid" and "polarizing" also come up, along with a lament about an "all-or-nothing" approach. These descriptions fit Cruz like a glove.

He has an impressive academic resume: an undergraduate degree from Princeton, followed by law school at Harvard. I've talked with his fellow students at Harvard and with his former colleagues from George W. Bush's 2000 presidential campaign. All of them mention how fiercely smart he is.

But the flattery stops there. They remember him as arrogant, sour and self-serving, traits that apply to his brief time in the Senate so far. In questioning Hagel during the nominee's confirmation hearing, he took a surprisingly, audaciously contemptuous tone.

Separately, in front of an audience of conservatives, he smirked dismissively as he griped that Hagel and John Kerry were "less than ardent fans of the U.S. military." Those two men fought in Vietnam, and earned Purple Hearts; Cruz never served.

Only three senators voted against Kerry's confirmation as secretary of state. Cruz was among them.

He belonged to the minority of 22 senators who voted against the Violence Against Women Act. He voted against suspending the debt ceiling for three months and against aid to victims of Hurricane Sandy.

He has already flagged his disagreement with the immigration reform proposal by a bipartisan panel of senators. He has already indicated antipathy to the new push for meaningful gun control.

Cruz has been quick to seize spotlights, like the one presented by "Meet the Press," and while newly minted senators often keep a relatively low profile, he reportedly holds forth in Senate conferences at great and off-putting length. And he's drawing unusual admonitions from senior Republicans.

"I think he's got unlimited potential," Sen. Lindsey Graham told Politico. "But the one thing I will say to any new senator - you're going to be respected if you can throw a punch but you also have to prove you can do a deal."

Indeed, the challenge for Republicans now - a challenge that, to limited and varying degrees, Rubio and even Eric Cantor are beginning to grasp - is to be seen and to act as a constructive force, as a party that's for things, that wants to be inclusive and that operates with a generosity of spirit, not an overflow of spite.

With his votes and his vitriol, Cruz undermines that. He brings himself plenty of attention. He'll bring Republicans nothing but grief.