Donald Trump's GOP Rivals Blast His Immigration Plan

— -- After Republican presidential candidate Donald Trump unveiled his six-page immigration policy paper earlier this week, his GOP rivals have wasted no time in lambasting his plan.

Florida Sen. Marco Rubio hit back against Trump today, saying that he doubts that Trump’s policies could ever become legislation.

Trump has called for a wall to be built across the southern border of the United States, and his plan seeks to "impound all remittance payments derived from illegal wages.” He has also pledged to end birthright citizenship.

But for the candidate who famously alluded to getting his military policy ideas from the Sunday political shows, any policy proposals are an easy target for other GOP hopefuls, who are eager to break Trump's lead in national polls.

When asked of Trump’s immigration plan at the Iowa State Fair today, Rubio said, "Most are really something I don't think has a chance to pass through Congress."

"Ultimately, we'll have to realistically deal with the fact that we have over 13 million people in this country illegally," Rubio added, "Most of them have been here for over a decade and I think Americans understand we're going to have to deal with that.”

Earlier this week, Jeb Bush, the once-frontrunner, dismissed Trump’s plans to build a wall and use remittances to pay for its construction.

“How do you revoke remittances?” he asked while campaigning in South Carolina on Monday. “A plan needs to be grounded in reality.”

Bush also pushed back on the birthright citizenship issue, telling CBS News , “That’s a constitutional right and Mr. Trump can say that he’s for this because people are frustrated that it’s abused. We ought to fix the problem rather than take away rights that are constitutionally endowed.”

He also added a not-so-veiled jab at how Trump comes up with policy. “I’m not going to fall into the trap of having, you know, say I watch 'Meet the Press' and get my foreign policy from that,” Bush said. “I think it needs to be a little more organized than that.”

New Jersey Gov. Chris Christie also weighed in, saying that walling off the entire southern border “doesn’t make any sense."

Christie also suggested that Trump’s business mogul status doesn’t make him qualified to make policy suggestions. “This is not negotiation of a real estate deal,” Christie told CNN. “This is international diplomacy and it’s different.”

Former Hewlett-Packard CEO Carly Fiorina called Trump's wall plan "completely unrealistic."

But not all GOP candidates have dismissed Trump’s plan.

Republican candidate John Kasich told ABC News today that though he said he hadn’t seen Trump’s immigration policy in detail, he did agree with certain tenants of it.

"I think we ought to be finishing the wall and making it clear that anybody that comes over once that’s done is going to be sent home, no questions asked,” Kasich said at the Iowa State Fair, adding that he does not, however, believe we should repeal birthright citizenship.

When asked on "Fox & Friends" his views on birthright citizenship, Christie said, “Everything should be on the table to be discussed to try to make sure that what we do is we get the most effective system we can to end what's been happening in this country.”

Scott Walker clearly endorsed ending birthright citizenship.

"We have to enforce the laws, keep people from coming here illegally, enforce e-verify to stop the jobs magnet, and by addressing the root problems we will end the birthright citizenship problem," Walker said in a statement, referring to the Web-based system that allows business to verify the eligibility of their employees to work in the U.S.