TRENTON -- In the next few days, presumptive Republican nominee Donald Trump is expected to pick a running mate, and the latest word from inside his campaign has it coming down to either Gov. Mike Pence of Indiana or Gov. Chris Christie.

Experts say who makes the cut will have everything to do with the type of race Trump wants -- or more likely, needs -- to run.

"If this campaign is about Donald Trump, Pence has the edge," said Frank Luntz, a Republican pollster. "But if it's a referendum on Hillary Clinton, Christie has the edge."

Unlike most prior presidential contests, a majority of Americans hold negative views of both the presumptive Republican and Democratic nominees, although slightly more Americans view Trump unfavorably than do Clinton.

As such, "the VP matters more in 2016 than in any other election cycle," said Douglas Brinkley, a presidential historian at Rice University and the editor of "The Reagan Diaries."

While both men are governors, it's actually their former jobs that offer the most help to Trump.

"The key component for Trump is credibility: Who adds the most credibility to Trump, and who most undermines the credibility of Clinton?" said Luntz, whose LuntzGlobal has conducted dozens of focus groups on the mogul's strengths and weaknesses.

"I'd argue that Pence probably adds the most credibility to Trump, and Christie takes away the most credibility from Clinton."

Pence, a former six-term U.S. Representative, would be able to help Trump shepherd legislation through the GOP-controlled House.

But Christie, a former federal prosecutor, is already helping Trump hold Clinton accountable for violating State Department security protocols and federal record-keeping laws.

Last week, the U.S. State Department reopened its investigation into Hillary Clinton's use of a private email server as secretary of state.

On Monday afternoon, Christie traveled to Virginia Beach, Va. with Trump and wasted little time showing his skills as a former federal prosecutor aimed at detracting credibility from Clinton.

"We had the spectacle last week of watching a director of the FBI, twice in one week, repeatedly say that the Democratic nominee for president lied," said Christie.

In testimony before the U.S. House Oversight and Government Reform committee last week, FBI director James Comey said that "we have no basis to conclude she lied to the FBI."

When the director was asked whether Clinton lied to the public, Comey demurred saying, "that's a question I'm not qualified to answer."

However, Christie had little difficulty answering the question for Comey on Monday.

"That's not a person who will stand for the rule of law," said the governor of Clinton. "That's a person who stand for the rule of her -- and that's not what we need in the White House."

Trump, following Christie onto the stage, insisted, "I am the law and order candidate."

If it sounded familiar, it's because it was the very same argument Christie had made last summer, while running for president himself.

In an interview with the Washington Post on Monday, Trump downplayed the significance of his choice of running mate, saying "History has said nobody ever helps."

But experts disagree, saying that whether Trump picks Pence, Christie, former House Speaker Newt Gingrich or someone else, they can't remember an election where a candidate's choice of VP was more crucial.

"This would be the first time that I can remember that a VP candidate has been so impactful that it allowed a candidate to win," said Reed Galen, deputy campaign manager to U.S. Sen. John McCain during his White House run in 2008. "No one was voting for Joe Lieberman or Dick Cheney."

Experts also say each VP choice before Trump represents a distinctly different strategic vision for the 2016 election.

"Choosing Christie would signal that Donald Trump is doubling down on his damn-the-torpedoes-take-no-prisoners scorched earth campaign style, and will continue to wage a consistently, maybe exclusively negative campaign, never leaving attack mode," said David M. Kennedy, the Pulitzer Prize-winning presidential historian and author of "Freedom From Fear: The American People in Depression and War."

"Choosing Pence would signal some sort of genuine effort to reach out to (more or less) reasonable Republicans, embrace someone who has experience in both Congress and a statehouse, has shown some flexibility on immigration and social issues, could perhaps help formulate and champion some constructive policies, and, whatever else might be said about him, is not a raving wing-nut," added Kennedy.

Brinkley suspects Trump will pick Pence "if he wants to unify the GOP," because the Indiana governor is "the darling of the GOP conservatives." But he also notes that geopolitics may play a role in helping boost Christie's chances.

As a social conservative, "Pence isn't going to get you a lot of centrist voters, whereas Christie puts Pennsylvania in play," said Brinkley, "and is much more media-savvy and a presence on the campaign trail."

Luntz thinks the distinctly different personalities of Christie and Pence both resonate with voters, albeit differently.

"Christie's the best debater of the bunch," said Luntz, "and creates the sound bites that matter and are memorable."

By comparison, Pence's personality, is "low-key, principled but pragmatic, and in my dial sessions, has always resonated," Luntz said, believing Pence "best to work across the aisle, and to offer a governing philosophy from someone who's actually done it."

Of course, the ever-mercurial, Trump may not decide to use either man for what they're best suited for.

"Remember: This is Trump," warned Galen. "Whomever he picks, I can easily picture him as being unhappy with them 20 minutes after he does it."

Claude Brodesser-Akner may be reached at cbrodesser@njadvancemedia.com. Follow him on Twitter @ClaudeBrodesser. Find NJ.com Politics on Facebook.