Story highlights Republicans focused their criticism on the legal case against Obama's immigration proposal

Republicans say the President is over stepping the legal boundaries of his authority

Obama addressed the nation in a prime time speech Thursday night

Opponents of President Barack Obama's plan, which makes sweeping changes to the nation's immigration system by use of executive order, focused their criticism on the legal case, saying Obama has overstepped the boundaries of his authority and is ignoring the will of the people.

Republicans started attacking the plan long before and soon after the President's prime-time address to the nation Thursday night, as GOP activists and lawmakers took to TV, their emails and their Twitter accounts to call out the commander-in-chief.

"By ignoring the will of the American people, President Obama has cemented his legacy of lawlessness and squandered what little credibility he had left," House Speaker John Boehner said in a statement after the speech. "His 'my way or the highway' approach makes it harder to build the trust with the American people that is necessary to get things done on behalf of the country. Republicans are left with the serious responsibility of upholding our oath of office."

Across the right, high profile Republicans -- including potential 2016 White House hopefuls -- vented their rage at an executive branch they see as out of control and out of touch.

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Former Florida Gov. Jeb Bush called Obama's action "ill-advised" and said it "undermines all efforts to forge a permanent solution to this crisis" that should come from Congress.

"President Obama has once again put divisive and manipulative politics before the sober leadership and sound laws required of an exceptional nation," Bush said in a statement. "It is time for Republican leaders in Congress to act. We must demonstrate to Americans we are the party that will tackle serious challenges and build broad-based consensus to achieve meaningful reforms for our citizens and our future."

Kentucky Sen. Rand Paul said he "will not sit idly by and let the President bypass Congress and our Constitution."

"President Obama is not above the law and has no right to issue executive amnesty. His actions blatantly ignore the Separations of Powers and the principles our country was founded on. The President has said 22 times previously that he does not have the power to legislate on immigration," Paul said in a statement.

The GOP seemed to take little comfort in Obama's explanation that his actions were in line with other actions past presidents had made.

"His actions are not only unconstitutional and in defiance of the American people who said they did not want amnesty in the 2014 elections, but they are also unfair to every immigrant who has come to our nation legally," Sen. Ted Cruz of Texas posted to his Facebook profile

Other Texas Republicans said that the President's actions were not only lawless but also ineffectual.

"The president's decision tonight will lead to more illegal immigration, not less," Texas Gov. Rick Perry said in a statement. "It is time for the president and Congress to secure our border, followed by meaningful reforms. There is no more time for political grandstanding."

Former Pennsylvania Sen. Rick Santorum, the second-place finisher in the 2012 battle for the GOP presidential nod and a potential 2016 contender, called the executive order "just another in a long line of power-grabs by this administration. Despite saying as recently as one year ago that he was not the 'emperor' of the United States, this President simply does not believe that the Executive is a co-equal branch of government."

Florida Sen. Marco Rubio, though, offered a more muted reaction -- focusing his criticism on how Obama handled the changes he announced Thursday night.

"We need immigration reform. But the right way to do it is to first bring illegal immigration under control by securing the borders and enforcing the laws, then modernizing our legal immigration system," Rubio said in a statement. "After we do these things, we will eventually have to deal with those here illegally in a reasonable but responsible way. The President's actions now make all of this harder and are unfair to people in our immigration system who are doing things the right way."

The attorneys general in Texas and Oklahoma both said they were planning lawsuits challenging Obama's authority to overhaul immigration rules without the approval of Congress.

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In Texas, Attorney General Greg Abbott, who is weeks away from becoming governor, said in a statement he is "prepared to immediately challenge President Obama in court, securing our state's sovereignty and guaranteeing the rule of law as it was intended under the Constitution."

Some Republicans were working on ways to block Obama from implementing his immigration order. Sen. Lindsey Graham of South Carolina posted on Youtube his case against the President's proposal

"I will try to defund the effort for him to go at it alone," Graham said in a video post Thursday night. "We will challenge him in court."

Others said they'll look to government funding bills. Louisiana Sen. David Vitter pledged on Twitter that he will do "everything I can" to stop Obama's move, "starting with removing any funding for amnesty."

Arizona Sen. John McCain said Obama's "executive fiat" hurts chances of working with a Republican-dominated Congress on an immigration reform bill.

He said in a statement that Obama's executive action "not only lacks legal justification, but will set back important bipartisan efforts to reform our broken immigration system and secure our nation's borders -- causes I have long supported."

Republican National Committee Chairman Reince Priebus -- who just two years ago, in the wake of the GOP's 2012 electoral defeat, endorsed a report that called on his party to support an immigration overhaul -- blasted Obama for both his policies and for acting as a "one-man legislature."

"The last time the President issued a politically motivated executive order to change our immigration laws, he precipitated a crisis at our border, leaving thousands of children at risk and ripping apart the families he claims to want to protect," Priebus said. "Granting amnesty does not secure our borders. Sadly, rather than trying to solve our country's immigration problems, the President's actions are intended to poison the legislative process at a time when he should be working to bring Americans together.