A Republican president may have to jump through hoops to undo key parts of President Obama's climate change agenda, but in the end, installing a new commander in chief may prove the easiest option for rolling back contentious emission rules.

Sens. Marco Rubio of Florida and Ted Cruz of Texas appear to be the most up for the job. They are two of the GOP's more aggressive presidential hopefuls with respect to their plans for repealing the centerpiece of the president's climate agenda, the Clean Power Plan.

Based on a review of their campaign policies, both candidates have made rolling back the Environmental Protection Agency rules a priority. But Rubio has become the more vocal of the two on repealing the plan once in the Oval Office.

The EPA Clean Power Plan requires states to reduce emissions by a third in the next 15 years. Sixteen states are champing at the bit to sue EPA over the plan in federal court, arguing that the rule oversteps EPA's authority and violates the Constitution.

Most candidates have some opinion on opposing the Clean Power Plan. Jeb Bush has come out against it, and so has New Jersey Gov. Chris Christie. But both are either looking to the courts for guidance, or want EPA to stay the rule and allow the market to dictate how emissions are lowered.

Rubio and Cruz, on the other hand, have been the most specific on moving swiftly to kill the plan as soon as they become president. "As president, I will immediately stop this massive regulation," says Rubio in a policy statement put out by his campaign.

There are also bills in the House and Senate, including some introduced by Cruz, to delay the plan until all litigation against it has concluded.

But most of the efforts in Congress are likely to fail because of the high percentage of votes required to make a bill immune to the president's veto power. The White House has said that President Obama would veto any measure sent to him that opposes the Clean Power Plan.

"With majorities in both houses of Congress, Republicans appear to have the votes to pass a joint resolution of disapproval to invalidate the plan under the Congressional Review Act, a statute that allows Congress to invalidate rules with a simple majority vote that is not subject to filibuster," wrote John Rego, executive editor with the international law firm Jones Day, in a recent analysis.

But much has changed in the Senate in the last five years to make it impossible for legislation to succeed, he said. Compared to 2010, it now takes a two-thirds vote of Congress "to prevail," especially as "ultimate success … will require 290 votes in the House and 67 votes in the Senate to override a certain presidential veto."

"Absent very vocal public opposition to the Clean Power Plan, it seems unlikely at this time that opponents would be able [to] attract sufficient votes," Rego said. Senate Majority Leader Mitch McConnell of Kentucky is said to be contemplating such a move, aides said.

Other bills to delay the plan face similar fights in the House and Senate, where Democrats support the president's plan and Republicans reject it, according to Rego.

But short of the Supreme Court vacating the entire rule, having a Republican president in office is the best bet to ensure the Clean Power Plan is repealed, observers said.

Jeff Holmstead, former head of the EPA air office under President George W. Bush, said repealing a rule can be difficult once it's set into motion. The Clean Power Plan was finalized on Aug. 3. But he said the plan is likely to be the exception to the rule.

"I have been involved in two presidential transitions from one party to another, and there are some regulations that are very difficult for a new administration to revoke or even modify, for legal or scientific or practical reasons," Holmstead said. "But the Clean Power Plan is not one of those regulations."

Holmstead said he is "quite confident" that "[i]f we have a Republican president on Jan. 21, 2017 … that the new administrator of EPA would revoke the Clean Power Plan, if it hasn't already been invalidated by the courts."

The reason for his confidence stems from the fact that the rule is not statutorily required under the Clean Air Act for EPA to proceed. Typically, rules that are defensible in court stem from an agency's underlying authority given to it by Congress.

Not being statutorily grounded also means environmentalists and states that support the plan will have a harder time suing the next administration to move the plan forward.

Holmstead said a new EPA administrator would have to go through some procedural hurdles, "and explain his or her rationale for revoking the rule," but in the end "this would be quite easy to do."

He said much of the rationale the next administration uses to upend the plan "would depend to some extent on where things stand in the litigation over the rule, but again, it would be quite easy for the next administration to simply undo the CPP entirely."

However, EPA Administrator Gina McCarthy thinks it will be much tougher, telling a group this summer that "[y]ou can not simply decide I am not implementing this." She based the statement on what is legally feasible based on the agency's interpretation of the law.

But environmental advocates and others concede that there are a number of ways a Republican president can hold back the rules, including simply not enforcing them.

This article appears in the Sept. 28 edition of the Washington Examiner magazine.