President Barack Obama on Tuesday delivered a passionate call for Congress to give his plan to close the Guantánamo Bay military prison a “fair hearing,” casting the terrorist detention center as a hindrance to national security.

Even before Obama spoke about the plan, Republican lawmakers dubbed it “illegal” and made clear it has almost no chance of being enacted. But Obama ended his remarks with a defiant tone.

“I don’t want to pass this on to the next president,” he said, flanked by Vice President Joseph R. Biden Jr. and Defense Secretary Ashton B. Carter. “I am absolutely committed to closing the detention facility at Guantánamo.”

Some legal and national security experts expect Obama will cite his war-making powers under the Constitution to issue an executive action to shutter Gitmo before he leaves office. The president did not respond to a shouted question from a reporter about a possible solo action as he exited the Roosevelt Room.

Obama said that during his first presidential bid in 2007 and 2008, closing the Guantánamo prison in Cuba had wide support among Republicans and Democrats. But, he said, that soon changed.

“Unfortunately, during [the] period when we were putting in place the pieces to close it, what had been bipartisan support suddenly became a partisan issue,” he said. “Suddenly, many who previously said it should close backed off because they were worried about the politics. The public was scared into thinking, ‘Well, if we close it, we’ll be less safe.’”

The commander in chief, a former constitutional law professor, said that is not the case.

He said trying most terrorism suspects in U.S. federal courts and then holding them in maximum-security prisons on American soil should be the country’s “preferred option.”

To that end, he vowed to “work with Congress to find a secure location in the United States to hold remaining [Guantánamo] detainees,” adding that maximum-security prisons in the U.S. have a “great record.” Obama said military commissions should only be used for detainees “captured on the battlefield,” saying other terrorism suspects should be tried in “our strong, proven federal courts.”

The plan does not point to specific maximum-security prisons in the United States to which detainees might be moved. But facilities in Colorado, Kansas and South Carolina were visited by Pentagon officials. It does, however, propose building a new prison at an existing military base inside the U.S.

That kind of domestic detention center is needed, Obama said, because the Guantánamo Bay prison is “counterproductive to our fight against terror” and because violent extremist organizations “use it in their efforts to recruit.” He called that not just his own opinion, but also “the opinion of experts” and “many in our military.”

Notably, the president said other world leaders — including heads of countries on which Washington depends for counterterrorism “cooperation” — often bring up Gitmo and specific detainees’ cases in private talks.

But the proposal landed with a thud on Capitol Hill, where Republicans are vehemently opposed to closing Gitmo and moving any of its prisoners to the United States.

Senate Majority Leader Mitch McConnell, R-Ky., has said previously he believes the Gitmo facility should remain open indefinitely, and many of his GOP colleagues agree.

“We’ll review President Obama’s plan, but since it includes bringing dangerous terrorists to facilities in U.S. communities, he should know that the bipartisan will of Congress has already been expressed against that proposal,” McConnell said Tuesday morning, shortly before Obama was set to speak.

Sen. Jerry Moran, R-Kan., was among the first to warn against the Obama administration attempting to implement the plan Tuesday morning.

“I remain committed to blocking the transfer of Guantánamo detainees anywhere in the United States, especially Fort Leavenworth. The critical mission of the Command and General Staff College in educating military members from ally nations across the world would be compromised,” Moran said in a statement that highlighted his seat on the Appropriations Committee. “We must safeguard the missions on Fort Leavenworth, the nearly 14,000 military and civilian personnel and their family members, and the thousands of Kansans who live in the Leavenworth community.”

Other Republican critics had begun to blast the Pentagon proposal even ahead of release.

Sens. Cory Gardner of Colorado, Tim Scott of South Carolina and Pat Roberts of Texas — all from states with potential Gitmo replacement facilities — continued to speak with one voice on the issue.

“Military leaders have repeatedly said they will not break the law to close the facility and relocate its prisoners on the mainland, which would be yet another of the administration’s misguided national security decisions,” the three senators said in a statement. “With ever-growing threats abroad and our increased efforts to combat ISIS, we need a place to house these terrorists, and that place is not in our communities, nor back on the battlefield.”

Sen. Kelly Ayotte, R-N.H., a member of the Armed Services Committee, added,“While the administration asserts that transferring detainees and closing Guantánamo is in America’s national security interests, they refuse to level with the American people regarding the terrorist activities and affiliations of the detainees who remain at Guantánamo,”

The White House spent much of Tuesday morning acknowledging that both their plan and their goal of closing the prison face steep uphill battles.

Obama said he is “very clear-eyed” about the hurdles of shuttering the Guantánamo detention facility, saying “the politics of this are tough.” He said Americans are afraid of terrorism and want suspects held in “some far away place.” Still, he had a message for lawmakers, saying the plan “deserves a fair hearing.”

Contact Bennett at johnbennett@cqrollcall.com and follow him on Twitter at @BennettJohnT.

Contact Lesniewski at nielslesniewski@cqrollcall.com and follow him on Twitter at @neilslesniewski.