Rand Paul was -- and is -- eager for the role. He was quick to break into the questioning early in the Fox News debate in Cleveland to attack Mr. Trump for his ties to Bill and Hillary Clinton. In the days since, he has ratcheted up his attacks, damning Mr. Trump as a fake Republican and a bully.
"If no one stands up to a bully, a bully will keep doing what he's doing," Mr. Paul said on Monday. "Unless someone points out the emperor has no clothes, he might walk right to the nomination. We might nominate a reality TV star if we're not careful. Someone needs to point out that the 'truth telling' coming from Donald Trump is bluster, non sequitur and self-aggrandizement."
That is a dead-on description of Mr. Trump on the stump. Unfortunately for Mr. Paul, his fact barrage has neither hurt Mr. Trump nor helped Mr. Paul's campaign. The Kentucky senator has slipped badly in polls and may not even be picked to stand with the top contenders on the debate stage at the Reagan Library in September. Meanwhile, Mr. Trump has sent out tweets tweaking Paul as a better doctor than a senator and insulting the man's golf game.
Former Texas Gov. Rick Perry and South Carolina Sen. Lindsey Graham have both berated Mr. Trump as well. Both their campaigns now look dead in the water. Jeb Bush has lectured Mr. Trump on his manners, but Mr. Trump continues to revel in baiting the ex-Florida governor by calling him "weak" and "a loser."
Marco Rubio, the fresh-faced Florida senator, limits his comments about Mr. Trump, saying he would not be able to talk about anything else if he answered every question he gets asked about the billionaire celebrity. No one else seems especially anxious to challenge The Donald -- no one, that is, but Fiorina.
By the numbers, ex-Hewlett-Packard CEO Carly Fiorina is the candidate who gained the most from her performance on the debate stage in Cleveland and she was not even in the main event. Stuck with the pack of seven laggard candidates in the preliminary "cocktail hour debate," Ms. Fiorina came on strong with the sharpest attacks on Mr. Trump's dubious conservative credentials. Subsequently, she has shot up in the polls and, in the eyes of Republican Party operatives, made herself the Wonder Woman who can hobble Mr. Trump's attention-grabbing candidacy by calling him out for his Neanderthal remarks about females.
The latest caustic exchange between Ms. Fiorina and Mr. Trump came when she blasted him for his weird comment about Fox News debate moderator Megyn Kelly. As the world knows, Mr. Trump said Ms. Kelly had blood coming out of her eyes and "wherever" when she hit him with a tough question about his crude characterizations of women. Many people, including Ms. Fiorina, interpreted "wherever" to mean Ms. Kelly was menstruating.
Telling CNN's Jake Tapper that women had no trouble identifying Mr. Trump's comment as pure sexism, Mr. Fiorina said, "I've had lots of men imply that I was unfit for decision-making because maybe I was having my period."
Mr. Trump was quick to send out a Twitter response: "I just realized that if you listen to Carly Fiorina for more than 10 minutes straight, you develop a massive headache. She has zero chance!"
So far, this grudge match is working for Ms. Fiorina by getting her the kind of media attention that may finally ignite her campaign. And Mr. Trump? He lives for this kind of trash talk. If the spat spills into September, the next debate could look like a retooling of "The Jerry Springer Show."
Two-time Pulitzer Prize winner David Horsey is a political commentator for the Los Angeles Times. Go tolatimes.com/news/politics/topoftheticket/ to see more of his work.