On the night before Christmas, Donald Trump attended midnight Mass, a service wishing peace and goodwill to all. But Trump's holiday spirit has its limits.

In a string of Twitter attacks, the Republican front-runner took credit for the Obama administration's plan to deport hundreds of illegal immigrants back to Central America, ridiculed Jeb Bush, and said, "I look forward to running against Hillary Clinton, a totally flawed candidate, and beating her soundly."

Does everyone see that the Democrats and President Obama are now, because of me, starting to deport people who are here illegally. Politics! — Donald J. Trump (@realDonaldTrump) December 25, 2015

Trump has used an unconventional playbook to dominate the race with insults and controversies. He's remained on top without pollsters or a single television ad.

Some cracks may be showing in Iowa, where Ted Cruz is ahead by nine points in the latest CBS News poll. The Texas senator spent the last week on a multi-state tour, complete with a Santa at every stop.

But it's possible that polls are underestimating Trump's support. A study earlier this week found he performed six points higher when people were polled online versus over the phone with a person on the other end.

One reason may be that voters are embarrassed to admit they're backing someone who's been criticized as a racist.

"Trump is a bit of an embarrassing person, and so if you think of yourself as serious minded voter and you like Trump, you're not going to want to tell people that," said CBS News political analyst Jamelle Bouie.

Bouie said Iowa will test a possible Trump effect.

"Iowa is place where unconventional candidates tend to do pretty well, and if Trump over performs in Iowa that gives us a guide post to what I think may unfold for the remaining season," he said.

The candidates are taking a rare few days off for Christmas, but they'll get back on the campaign trail starting Sunday with just five weeks to Iowa.