WASHINGTON - Flanked by victims of sex trafficking and their families, President Donald Trump on Wednesday signed a bill co-authored by Ohio Republican Sen. Rob Portman that establishes fines and prison terms for operators of websites that engage in online sex trafficking.

"I'm signing this bill in your honor...You have endured what no person on earth should have to endure and we are going to do everything in our power to make sure that traffickers are brought to a swift and firm justice," Trump told the victims.

Yvonne Ambrose, a Chicago woman whose 16-year-old daughter was murdered by a man who used Backpage.com to buy her for underaged sex, teared up as she thanked the president for signing the legislation.

"It means so much to our family," she said. "Hopefully there won't be any more people who have to endure that pain."

"We're with you a thousand percent, OK? ," the president told her.

The bill Portman co-authored clarifies that the Communications Decency Act doesn't protect online sex trafficking, and prosecutors and sex trafficking victims can take those website operators to court. It makes it a crime for someone to use a website "with the intent to promote or facilitate the prostitution of another person..."

Portman delivered remarks at the signing that credited tweets from Ivanka Trump early in the administration for adding fuel to the drive for passage.

#SESTA will help ensure justice for trafficking victims & survivors. I was honored to stand alongside my friend from #Ohio, trafficking survivor and founder of Save Our Adolescents from Prostitution (SOAP) Theresa Flores, as @POTUS signed #SESTA into law today at the White House. — Rob Portman (@senrobportman) April 11, 2018

"This is a momentous day in the fight to help stop online sex trafficking, and a big victory for trafficking victims and survivors who for too long have been denied the opportunity to get the justice they deserve," said a statement Portman released after the bill was signed.

The legislation was signed several days after the U.S. Department of Justice seized Backpage.com, which it described as "the Internet's leading forum for prostitution ads, including ads depicting the prostitution of children," and filed criminal charges against seven people affiliated with the website.

Much of the material in the Justice Department's 93-count indictment came from an investigation of the website that was produced by a congressional committee chaired by Portman.

Although the Justice Department was able to prosecute Backpage.com's operators on the basis of pre-existing law, Portman said the bill Trump signed Wednesday is needed so victims can bring civil lawsuits against sex-trafficking websites, and to allow prosecution at the state and local level.

"There are lots of Backpages out there," said Portman, who predicted a flurry of lawsuits around the country enabled by the legislation. "As soon as you shut down one site, another pops up. There is much more to do."