By Senator Dianne Feinstein

Originally appeared in the New York Times

INSTEAD of blocking President Obama’s efforts to close the costly Guantánamo Bay detention facility, Congress should be working with him to finally shut it down.

I’ve been to Guantánamo twice, once in 2002, with the former defense secretary Donald H. Rumsfeld and other senators, and again in 2013, with Senator John McCain, Republican of Arizona, and Denis R. McDonough, the White House chief of staff.

Seeing the facility firsthand reinforces my belief in the great need to close this prison, which has cost us billions of dollars and is a real threat to our national security.

Simply put, Guantánamo is one of the best propaganda tools that terrorists have today. Our enemies use it to justify terrorism and recruit others to carry out violent jihad, and our allies continue to criticize it as a violation of the rule of law.

It’s no coincidence that the Islamic State, also known as ISIS or ISIL, dresses its victims in the same orange prisoner suits used in Guantánamo before conducting their ghastly beheadings. Our policies have allowed terrorists to cloud who holds the moral high ground.

President George W. Bush said that he wanted Guantánamo to be closed. So did the former secretaries of state Condoleezza Rice and Colin L. Powell, as well as the former secretaries of defense Robert M. Gates and Leon E. Panetta, among others.

In addition to being a terrorist recruiting tool, Guantánamo is a huge drain on taxpayer dollars.

The cost per detainee at Guantánamo is 30 times more than that of the most secure detention facilities in the United States. It’s hard to justify spending more than $2.5 million per detainee when it costs just $86,374 to hold an inmate in the so-called Supermax federal penitentiary in Colorado.

Even if one can get past the national security, legal and moral concerns about holding individuals for an indefinite amount of time without charge or trial, there’s simply no getting around the fact that Guantánamo is a huge waste of money.

So what have we achieved by spending around $400 million a year to run detention operations at Guantánamo?

During the Bush administration, 779 people were brought to Guantánamo, all without charge. Over time we’ve learned that many were simply at the wrong place at the wrong time and shouldn’t have been detained in the first place.

Most detainees — 532 to be exact — were released by the Bush administration. Of the 112 detainees who remain today, only about 10 have been convicted or charged with a crime in the military commissions.

Shockingly, the five co-conspirators charged with planning the Sept. 11 attacks have still not gone to trial, despite the filing of charges years ago.

Equally troubling: All of the convictions that came from military commissions resulted in light sentences, are currently being appealed or have been overturned entirely.

Contrast that with the record of the federal criminal courts. Between Sept. 11 and the end of 2014, civilian courts prosecuted 580 terrorism-related cases, with a conviction rate of around 90 percent.

One thing has become clear: Keeping detainees at Guantánamo indefinitely hasn’t worked.

Senator McCain has called on the White House to deliver a plan to close Guantánamo. I join with him.. In particular, we need a proposal for bringing detainees to the United States and holding them securely for as long as necessary. But no matter what comes out of the White House, the next steps Congress must take are clear.

First, we need to amend this year’s defense authorization bill so that the 53 detainees already cleared for transfer can be securely removed from Guantánamo and sent to their home countries or other nations.

President Obama has vetoed an initial version of that bill, in part because of unreasonable limitations on transferring detainees to other countries, so Congress now has a chance to revise those limitations.

Second, Congress should lift the current ban on transfers to the United States so detainees can be tried in federal criminal courts and held in federal prisons. Federal prisons already hold Al Qaeda terrorists like Zacarias Moussaoui, the “shoe bomber” Richard Reid and the “underwear bomber” Umar Farouk Abdulmutallab.

Third, for those relatively few detainees who can’t be tried because of a lack of evidence but still need to be held until the end of hostilities, bringing them to the United States presents a more cost-effective option.

Facilities in the United States are up to the task. There’s no reason to think a Guantánamo detainee is any more likely to escape from Supermax than any other federal prisoner. It hasn’t happened before, and there’s no reason to think that would change.

Congress should take tangible steps to close Guantánamo.

Dianne Feinstein is a Democratic senator from California and the vice chairwoman of the Select Committee on Intelligence.