The prospect of a Trump-Rubio rumble and 3 other things to watch for in the Republican debate

Their field now narrowed to five, the Republican presidential candidates square off Thursday for their 10th debate, but one dynamic remains the same: Can any other candidate gain on front-runner Donald Trump?

Taking on Trump will probably fall to Ted Cruz, the Texas senator who has been more willing to engage in direct battle with the celebrity billionaire than his close rival, fellow Sen. Marco Rubio of Florida. Both men are struggling to emerge from Trump’s shadow as the GOP’s best alternative as the race heads to Super Tuesday, the prized collection of delegates in mostly Southern states. But their ascent is being complicated by the still fluid field, including Ohio Gov. John Kasich and retired neurosurgeon Ben Carson, who both will still compete in the March 1 contests.

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Here are a few things to watch for.

Will Rubio rumble with Trump?

While the GOP establishment is throwing money and clout behind Rubio’s campaign as an antidote to Trump, the first-term senator has declined to tackle him head-on. Some strategists say he must, if he has any hope of cutting down Trump’s lead and actually scoring a win in a state. But Rubio has preferred to outsource those attacks as he focuses on weakening Cruz. Plus, Trump hits back. Will Rubio jump in the Trump ring?

Can Cruz get past the liar label?

Cruz’s campaign sputtered over the last week as Trump and Rubio both criticized his hardball campaign tactics, repeatedly calling him a liar. For a candidate whose campaign poster reads “Trusted (Get it? Trust Ted?), this posed a problem. Religious voters are crucial to Cruz’s strategy to win Southern states, and he fired a top advisor this week to assign responsibility for the tactics. Watch for him to work hard Thursday night to try to regain voters’ trust.

Immigration, immigration, immigration

It doesn’t matter which part of the country the candidates are stumping in, immigration is often tops on voters’ minds. But at Thursday's debate in Houston, it may dominate. Who will talk toughest on immigration policy? Trump once set himself apart, with his promise to build a “beautiful� wall along the Mexico border and send “back� the estimated 11 million people here illegally. But Cruz now says he, too, would round up and deport them. Will Rubio join in? Look for the candidates to break new ground on an old issue.

It’s still a five-man race

Keep an eye on Kasich and Carson, who may not be tops in the polls, but still have punch to give. Kasich has struck a note with his more moderate conservatism, and will be playing not necessarily to the debate audience in Texas, but to viewers in Michigan and the Northeastern states also going to the polls next week. Carson is highly popular among religious voters in the South. Watch to see if they disrupt the momentum of the top three. Or not.

Twitter: @lisamascaro

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