Former GOP front-runner derides Trump's plan as unrealistic.

Republican presidential candidate Jeb Bush is dismissing front-runner Donald Trump's immigration plan as impractical and destined to fail.

It's Bush's latest attempt to move up in the national polls and revive his candidacy. This time, his strategy is based on taking the offensive and portraying himself as a pragmatic, realistic leader while he suggests that Trump is living in a dream world.

"A plan needs to be grounded in reality," the former governor of Florida told the Washington Post Monday night while campaigning in South Carolina.

Bush said it's impractical for Trump to propose erecting a wall between the United States and Mexico and to propose having the Mexican government pay for it. Similarly, Bush derided Trump's threat to seize remittances sent by undocumented workers to their families in Mexico and Trump's threat to end birthright citizenship. Trump also wants to send millions of such workers and their families back to their countries of origin, which Bush opposes.

Bush favors a more lenient approach that includes creating a pathway to earned legal residency for millions of people who entered the United States illegally.

"We've got to control the border," Bush told the Post. "We've got to enforce the rule of law. We've got to deal with extended stays on legal visas. We've got to have an e-Verify system [an Internet-based system that allows employers to obtain information on prospective employees' legal status] that's verifiable. We've got to deal with sanctuary cities. We've got to forward-lean on the border. There's practical things that we can do to reduce the flow of illegal immigrants, which clearly is important to do,"

Bush recently lost his position as the front-runner for the 2016 Republican presidential nomination. Bush has the support of only 9 percent of GOP voters, dropping him to fourth place, according to a new Fox News poll. Billionaire real-estate developer Trump is in first place with 25 percent; retired neurosurgeon Ben Carson is second with 12 percent, and Sen. Ted Cruz of Texas is third with 10 percent.