*Editor's note: This story has been updated throughout.

President Obama on Thursday made good on his promise and said he will use his executive authority to grant millions of undocumented immigrants a work permit and a reprieve from deportation proceedings.

About an hour before his official announcement, the White House released a fact sheet detailing how more than 4 million people — specifically the undocumented parents of legal residents or U.S. citizens — will be shielded from deportation.  

Reactions from Republicans were swift and anticipated, following a week of outrage including threats of everything from impeachment to a government shutdown.

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U.S. Sen. John Cornyn, R-Texas, said on the U.S. Senate floor Thursday that the action would lead to additional surges of would-be illegal border crossers who interpret the president’s move as a sign that “it's okay to come."

"As I said earlier, this is also a major boon to the cartels and other gangs who control Mexico's smuggling networks,” he added. “And it will almost certainly lead to thousands of people who've committed crimes in this country gaining legal status.” 

Texas Attorney General and Gov.-elect Greg Abbott promised to "immediately challenge President Obama in court."

Obama's order means sweeping changes are coming for a portion of Texas’ 1.46 million undocumented immigrants, the second most behind California, according to the latest estimates by the Migration Policy Institute, a Washington-based think tank and research firm. There are about 11.4 million undocumented immigrants in the United States.

The undocumented parents of  children in the country legally are eligible for a reprieve from deportation proceedings if they pass background checks, pay taxes and have been in the country for more than five years, according to the White House. That one measure could affect as many as 533,000 undocumented immigrants in Texas, about 40 percent of the state’s unauthorized population. Another 92,000 reside with children who are not citizens but could be in the country legally.

"Individuals will have the opportunity to request temporary relief from deportation and work authorization for three years at a time if they come forward and register, submit biometric data, pass background checks, pay fees and show that their child was born before the date of this announcement," the White House said in its statement.

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In all, about 1.15 million of Texas’ undocumented immigrants have lived in the country for at least five years, including about 218,000 immigrants who have lived here for more than 20 years.

They will not qualify for citizenship, however, since that would require Congressional action, the president said. If Congress passes a comprehensive immigration bill, he added, the actions he is taking this week would no longer be policy.

“To those members of Congress who question my authority to make our immigration system work better, or question the wisdom of acting where Congress has failed, pass a bill,” he said. “The day I sign that bill into law, the actions I take will no longer be necessary.”

Under the White House plan, a 2012 initiative called Deferred Action for Childhood Arrivals, or DACA, will also be expanded. That program provides younger undocumented immigrants a work permit and a two-year reprieve from deportation proceedings.

Currently, DACA applicants must have been in the U.S. continuously since June 2007, must have arrived in the country before they were 16 and must have been 30 or younger as of June 2012. The new policy is likely to broaden the pool of potential applicants by changing the arrival date to including people who arrived before January 2010. The relief will be available for three years instead of the current two. 

The administration will also expand work authorization for high-tech workers waiting on "legal permanent residency" status, or green cards.

The president announced Thursday that border enforcement, too, will undergo a series of overhauls, beginning with the abolishment of the Secure Communities program, which is administered by Immigration and Customs Enforcement. It compares the fingerprints of people arrested to a federal database to determine if the arrestees are eligible for deportation under federal immigration laws.

Critics of the program have claimed it flags for deportation immigrants who have committed minor crimes, like traffic violations. That program will be replaced with a "new Priority Enforcement Program (PEP) to remove those convicted of criminal offenses," the White House said in a news release.

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Obama said people who came into the country recently will not be eligible for the program, and greater efforts will go toward faster deportations of people who recently entered the country illegally.

Proponents of Congress passing a comprehensive immigration overhaul bill that offers broader protections and eventual citizenship said that Obama's executive action is a start. But they remain wary of what happens after he leaves the White House.

“The new president has to reissue an executive order, or at least not repeal it,” Fernando Garcia, the executive director of the El Paso-based Border Network for Human Rights, said at a press conference on Tuesday. “This is limbo status, a piece of paper that allows you to work or not be deported. We’re very concerned that people will be left out.”

Jackie Watson, an Austin-based immigration attorney, said how many people are eligible to remain in the U.S. under Obama's plan depends on several factors, including minor details that she said could make or break a person’s claim. Assuming that every undocumented parent would be eligible is flat-out wrong, she said.

Watson added that the vetting process for applicants under Obama's order would likely be more thorough than what it currently is for recipients of DACA.

“I am worried about what the criminal exclusion grounds will be,” she said. “It could be something [as minor] as not having a driver’s license or insurance.”

Republicans, meanwhile, went on the immediate offensive upon the release of Obama's plans, though they'd been fired up over it all week. 

In a letter to the president on Wednesday, U.S. Rep. Michael McCaul, R-Austin, joined U.S. Rep. Bob Goodlatte, R-VA and the chair of the House Judiciary Committee, in demanding the president abandon his plans.

“Let’s secure the border, enforce our immigration laws in the interior of the United States and build a broad consensus for immigration reform,” McCaul, the chairman of the House Homeland Security Committee, wrote. “Otherwise, as the chairmen of the committees with oversight over border security and our nation’s immigration laws, we will be forced to use the tools afforded to Congress by the Constitution to stop your administration from successfully carrying out your plan.”

Last week, Texas Attorney General and Gov.–elect Greg Abbott said: “If the president uses what seems to be his version of dictatorial powers to impose on Americans a law that is not passed by the United States Congress, I think any and all possible actions should be taken to try to stop it, including potential legal action.”

Gov. Rick Perry doubled down on that on Wednesday and said there would be “a very real possibility” the state would sue to stop the president’s plan from becoming actual policy.

Texas’ border Democrats are standing behind the president, however. They claim the U.S House could have acted on a bipartisan measure that the U.S. Senate passed in June 2013.

‘The House never took it and that was very frustrating after we had indications that they would,” said U.S. Rep. Henry Cuellar, D-Laredo. “Two out of the last three Republican presidents took executive orders to do almost the same thing that the president is going to do. I prefer Congress, I think we could do more. But under the circumstances the president did warn the Republicans he was going to do this.”

U.S. Rep. Filemon Vela, D-Brownsville added: “Given the political realities in Washington, it is highly unlikely that meaningful immigration reform gets passed in the next two years in Congress without conditioning a pathway to citizenship on unattainable border security measures.”

Since 1956, executive action has been used more than 35 times to affect immigration laws, including 19 times since George H. W. Bush was president in 1990, according to the American Immigration Council. Bush's actions that year deferred deportation for 1.5 million undocumented immigrants that weren’t covered by President Ronald Reagan’s 1986 immigration reform bill.