WASHINGTON — President Obama’s new immigration program was supposed to begin accepting applications Wednesday from thousands of illegal immigrants hoping for relief from the threat of sudden deportation. Instead, the administration abruptly postponed its launch after a federal judge in Texas temporarily blocked implementation of the initiative.

In a decision late Monday, U.S. District Judge Andrew Hanen ruled that the deferred-deportation program should not move forward while a lawsuit filed by 26 states – including Maine – challenging it was being decided. Though Hanen did not rule on the constitutionality of Obama’s November immigration order, he said there was sufficient merit to warrant a suspension of the program while the case goes forward. All told, Obama’s immigration actions are projected to benefit as many as five million immigrants, many of whom could receive work permits if qualified.

The effects of Hanen’s procedural ruling rippled through Washington and underscored a broader challenge to the president as he seeks to solidify the legacy of his administration.

Along with immigration, the fate of two of Obama’s other signature initiatives – a landmark health care law and a series of aggressive executive actions on climate change – now rests in the hands of federal judges. It’s a daunting prospect for a president in his final two years who believes he is on the path to leaving a lasting impact on intractable and politically perilous issues, despite often bitter relations with Congress.

Now, Obama and his Republican antagonists in Congress face the uncertainty of having their disputes mediated by the courts. In an appearance in the Oval Office on Tuesday, Obama told reporters: “The law is on our side and history is on our side.”

This is not the first time where a lower court judge has blocked something or attempted to block something that ultimately is going to be lawful,” he added, “and I’m confident that it is well within my authority” to execute this policy.

The immigration fight will likely head next to the U.S. Court of Appeals for the 5th Circuit as the White House vowed to quickly appeal Hanen’s ruling. In the meantime, Homeland Security Secretary Jeh Johnson said Tuesday his agency would postpone plans to begin accepting applications for the new program, which would expand a 2012 program that defers deportations of immigrants who came to the United States illegally as children. (The 700,000 people who have already benefited from that program are not affected by Hanen’s ruling.)

A second, much larger, program designed to protect from deportation the undocumented parents of U.S. citizens and permanent legal residents was not to begin taking applications until late May and its future remains uncertain.

HEALTH CARE, CLEAN AIR ALSO IN THE COURTS

On health care, the Supreme Court will hear arguments next month in King v. Burwell, a case that calls into question whether millions of people who have bought coverage on federal exchanges are entitled to subsidies.

In April, the U.S. Court of Appeals for the District of Columbia Circuit, just one rung below the Supreme Court, will hear three consolidated cases challenging the Environmental Protection Agency’s right to use a provision of the Clean Air Act to regulate greenhouse gas emissions from power plants.

“The Supreme Court’s docket in recent terms looks a lot like an outline for a stump speech for a 2016 (presidential) candidate,” Doug Kendall, president of the Constitutional Accountability Center, said in an email. “The Court is deciding just about every major question that divides Americans along ideological lines.”

In addition to the ongoing immigration suit from the 26 states – 24 of which are led by GOP governors – House Republicans are considering filing their own suit against the administration over its immigration actions.

DEMOCRATs PREPARED FOR CHALLENGES

One senior Senate Democratic aide, who asked for anonymity in order to discuss party strategy, said one reason Senate leaders pushed so hard last Congress to seat Obama’s nominees on the D.C. Circuit was because “having judges who may be more sympathetic to the administration’s view is not an insignificant way of safeguarding against” legal reversals.

Last Congress, the Senate confirmed four of Obama’s nominees to the D.C. Circuit, which hears many challenges to executive actions: Democratic appointees now outnumber Republican ones there, 7 to 4.

On immigration, Democrats and Republicans scrambled Tuesday to determine how Hanen’s ruling would affect a showdown over GOP demands to make funding for the Department of Homeland Security, which expires next week, contingent on halting Obama’s ‘deferred action’ program. The White House has threatened to veto any legislation if it contains language overturning the president’s immigration programs. Such a veto could lead to a partial DHS shutdown.

Obama issued his immigration orders shortly after the midterm elections in November, saying he could no longer wait on Congress to reform border control laws that have left more than 11 million illegal immigrants in limbo. An effort to pass a comprehensive immigration reform bill failed last summer.

But in his lengthy memorandum opinion, Hanen ruled that no law gave the administration the power “to give 4.3 million removable aliens what the Department of Homeland Security itself labels as ‘legal presence.’ In fact, the law mandates that these illegally-present individuals be removed.”

Hanen’s decision was a major, if temporary, defeat for the administration, which argued that the case should be thrown out because it was “based on rhetoric, not law.”

“This ruling underscores what the president has already acknowledged publicly 22 times: He doesn’t have the authority to take the kinds of actions he once referred to as ‘ignoring the law’ and ‘unwise and unfair,’ ” Senate Majority Leader Mitch McConnell, R-Ky., said Tuesday.

The White House has said the president’s actions were based on the practice of “prosecutorial discretion,” which allows law enforcement agencies with limited resources to set priorities.

Hanen based his temporary injunction on his belief that the administration, in making such a broad change to what current law “mandates,” at least did not comply with the Administrative Procedure Act, the nearly 70-year-old stature that governs how federal agencies implement regulations.

Immigration advocates charged that Hanen had “cherry-picked” his ruling and said they would urge immigrants to keep preparing their applications.