When Jeb Bush campaigners came across an undecided Republican in New Hampshire, they simply called his mom.

The former Florida governor's staffers told the Washington Post that putting Barbara Bush, the former first lady and mother of the Republican candidate, on the phone usually convinced the voter.

This level of family involvement marks a shift in Mr. Bush's campaign, and he evidently hopes it will shift voters as well.

It may not be as tough a sell as it looks, as family ties may impact voters subconsciously more than they even realize, says Doug Wead, historian and author of "All the President's Children," a book about family involvement in political campaigns.

"The voter is not actually a very good expert on why they have voted the way they have, that is, they may have been influenced whether they know it or not," Mr. Wead writes in an e-mail to The Christian Science Monitor. "And so family members may indeed have influence."

He points to the familial success of the Kennedys or Richard Nixon, who was told by a political enemy during Watergate, "If you've raised two daughters like that you can't be all bad."

In a campaign where voters seemd to favor political outsiders with minimal governing experience, Bush understandably kept the focus off his family ties at first. For one thing, his mother's early comments were hardly complimentary, as she famously told NBC's Today show, "We’ve had enough Bushes."

Mother and son have resolved their difference of opinion; in addition to taking phone calls, Ms. Bush appeared alongside her son at a town hall meeting in New Hampshire before the primary election.

"Barbara Bush is the most popular Bush and a reminder of what is good about the family," Wead says. "So, of course, [Jeb Bush] will wrap himself with his mom."

Initially, Jeb was not expected to call for help from the nation's 43rd president. That seems to have changed as well.

Former President George W. Bush intends to join his brother's campaign in earnest with a South Carolina rally on President's Day, Philip Rucker and Ed O'Keefe reported for the Washington Post. The former president has said that given the uncertainty of this unusual race, a surprise showing in South Carolina could boost his brother's campaign.

“Donald Trump and anybody else who wants to be critical of George W. Bush, I hope they do it, because the people of South Carolina are sick and tired of people tearing down George W. Bush,” Jeb Bush said on Brian Kilmeade's radio show on Friday.

Polls currently give Donald Trump 37.3 percent of the South Carolina primary vote, while Bush comes in fourth at 9.3 percent, according to Real Clear Politics. But Trump's success thus far has been at the expense of Republican traditionalists.

If Bush does well in the Feb. 20 primary, it could indicate that an "Old Guard" in the Grand Old Party is willing to fight back against the anti-establishment populism that has kept Trump, a former Democrat disliked by Republican leaders, at the top of the polls.

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Bush's next test is to prove himself in Saturday night's CBS Republican debate, where his biggest challenge is "finding a way to attack Mr. Rubio," wrote Reid Epstein for The Wall Street Journal, referring to Florida Sen. Marco Rubio.

"Mr. Bush survived a near-death experience by besting Mr. Rubio in New Hampshire, and now he needs to build off his last two strong debate performances," Mr. Epstein wrote. "Mr. Bush has to play to the pundits to keep his donors satisfied and find a way to contrast his experience with Mr. Rubio’s and his conservative bona fides with Mr. [John] Kasich’s."