President Trump signed a bill Wednesday allowing terminally ill patients access to experimental medical treatments not yet approved by the Food and Drug Administration (FDA).

Dubbed "right to try," the law's passage was a major priority of Trump and Vice President Pence, as well as congressional Republicans.

"Thousands of terminally ill Americans will finally have hope, and the fighting chance, and I think it's going to better than a chance, that they will be cured, they will be helped, and be able to be with their families for a long time, or maybe just for a longer time," Trump said at a bill signing ceremony at the White House, surrounded by terminally ill patients and their families.

Trump thanked lawmakers sitting in the audience who sponsored the bill, including Sen. Joe Donnelly, a vulnerable Democrat up for reelection in Indiana.

Despite calling Donnelly a "really incredible swamp person" earlier this month, Trump thanked the senator for his work on the bill.

Sen. Joe Manchin (W.Va.), another vulnerable Democrat up for reelection, was the only other Democratic co-sponsor on the bill, but did not attend the ceremony because he is in West Virginia this week, his office said.

Congress is on recess this week for Memorial Day.

Most Democrats and public health groups oppose the bill, arguing that it could put patients in danger.

"FDA oversight of access to experimental treatments exists for a reason - it protects patients from potential snake oil salesmen or from experimental treatments that might do more harm than good," said Rep. Frank Pallone Jr. (D-N.J.), ranking member of the House Energy and Commerce Committee.

Opponents also argue it gives "false hope" to patients, since drugmakers aren't required to give unapproved medicines to patients who ask for them.

Supporters say, however, it will provide new treatment opportunities for terminally ill patients who have exhausted existing options.

"While a long time coming, today is a monumental win for patients desperately seeking the 'right to try' investigational treatments and therapies," said Energy and Commerce Committee Chariman Greg Walden (R-Ore.) and health subcommittee chairman Michael Burgess (R-Texas).

"With 'right to try' being the law of the land, we are confident that the Trump Administration, and FDA Commissioner [Scott] Gottlieb, will take both congressional intent and the safety of patients into consideration when implementing this important law."