 -- Hillary Clinton has been bringing out the big guns when it comes to her surrogate supporters — including President Barack Obama, first lady Michelle Obama and Vice President Joe Biden.

At the same time, GOP candidate Donald Trump appears to be leaning less on the heavy hitters he touted earlier in the campaign, including former rivals Dr. Ben Carson and New Jersey Gov. Chris Christie, as well as former Speaker of the House Newt Gingrich.

The differences in the surrogate game between the campaigns appear stark just two weeks before the election.

On Trump's side, Carson is still making appearances on TV and the trail, though significantly less frequently. Gingrich was a public part of the surrogate crew but has virtually disappeared from the roster, though he is still posting on social media about Trump and writes op-eds for Fox News that praise him.

Christie, who also used to make regular public appearances — speaking on cable news shows or introducing Trump at rallies — is still a part of the campaign and a constant presence behind the scenes, though he has effectively stopped making public appearances.

While Christie is still a frequent guest at Trump Tower in New York, his former full-throated defense of Trump appears to have moderated, as seen when he was recently asked if he was proud of the campaign that Trump was running.

"Listen, for me, the person who needs most to be concerned about the kind of the campaign they’re running is the candidate, because it’s the candidate’s campaign ... I'm proud of everything I've said, and that's all that I can control. The rest of it I can't control," Christie told NBC last week.

Christie and Gingrich, who were both considered as Trump's running mate, were arguably two of his best-known surrogates, and while they still make some appearances, the frequency and vigor of those appearances has decreased.

Former New York City Mayor Rudy Giuliani has been a strong and consistent supporter of Trump, even lately. Giuliani made several morning show appearances on the day of the second Clinton-Trump debate, shortly after the release of a 2005 recording in which Trump is heard bragging that he can grope women without their consent.

Giuliani will appear on the campaign's new "Trump Tower Live" program tonight.

John Hudak, a senior fellow at the Brookings Institution, said that there has been a change in Trump's surrogate operation since the Republican National Convention in July.

"That shift is remarkable, and I think it's happening for one of two reasons. One is that these surrogates are looking at the writing on the wall and trying to quietly distance themselves from a campaign that is clearly losing," Hudak told ABC News.

"The other is that Trump doesn't think that they're being effective and he is pulling them from the trail because he doesn't think that they're doing a good job," he said.

There are two reasons Clinton could be pulling out all her heavy hitters in recent weeks, which also include former rival Sen. Bernie Sanders and most recently Sen. Elizabeth Warren, who spoke before Clinton in New Hampshire on Monday.

"She's doing two things by bringing out all of the high-powered surrogates. One is really crafting an effective get-out-the-vote campaign. These are not just popular Democrats, but they are people who really know how to bring out the troops," Hudak said.

He continued, "The other is she probably assumes she will be president and now needs that turnout effort to get herself a Democratic Senate. And for some, that's an easier sell because even Democrats who are skeptical of her — including possibly Warren, Sanders and even Biden — can be more easily coaxed to come help when the Senate is on the line."