Ryan Wesley Routh, suspect in apparent assassination attempt of Trump, in federal court as investigators search for motive

Ryan Wesley Routh, the suspect in the apparent assassination attempt of Donald Trump, is in federal court for an initial appearance Monday morning.

Routh is wearing dark prison scrubs, and his feet and hands are shackled. He will appear before Magistrate Judge Ryon M. McCabe.

Federal prosecutors have not yet announced what charges Routh will face. He was taken into custody Sunday after being stopped on the highway following the shooting incident.

Former President Donald Trump thanked law enforcement for an “incredible” response to what the FBI has described as an assassination attempt at Trump’s Palm Beach, Florida, golf course on Sunday.

Multiple law enforcement sources told ABC News that the 58-year-old suspect, Ryan Wesley Routh, was detained by Florida authorities in relation to the incident. Authorities are now probing for more details on the would-be shooter.

“I would like to thank everyone for your concern and well wishes – It was certainly an interesting day!” Trump said in a post on Truth Social.

“Most importantly, I want to thank the U.S. Secret Service, Sheriff Ric Bradshaw and his Office of brave and dedicated Patriots, and, all of Law Enforcement, for the incredible job done today at Trump International in keeping me, as the 45th President of the United States, and the Republican Nominee in the upcoming Presidential Election, SAFE.”

“THE JOB DONE WAS ABSOLUTELY OUTSTANDING. I AM VERY PROUD TO BE AN AMERICAN!” he wrote.

Photo of Routh following his detention by authorities in Florida.

Martin County Sheriff’s Office

The former president is expected to meet Monday with the acting director of the Secret Service, Ronald Rowe Jr., sources familiar with the matter told ABC News.

Following the July 13 assassination attempt on Trump at a campaign rally in Butler, Pennsylvania, Trump, who was shot in the ear, also met with the former director, Kimberly Cheatle, at the time for a briefing.

On Sunday afternoon, Secret Service agents accompanying Trump fired at a man armed with an AK-47-style rifle on or near the Trump International golf course on Sunday.

The FBI is investigating Sunday’s incident as an “attempted assassination.” Palm Beach County Sheriff Ric Bradshaw said at a news conference Sunday afternoon that the gunman was within 300 to 500 yards of Trump when he was spotted.

Secret Service agents fired four to six rounds at him before he dropped his weapon and fled the scene in a vehicle. Witnesses reported the license plate number to authorities, and the suspect was stopped and detained.

It was not clear if the suspect was aiming his gun at the former president. Agents fired at the suspect after spotting his rifle through the fence line, multiple sources told ABC News.

Sources said three shell casings believed to be associated with the suspect’s AK-47 were found on the scene, though investigators are still evaluating whether the suspect fired his weapon. The rifle and two backpacks containing a GoPro camera and ceramic tiles were recovered from the scene, Bradshaw said.

Authorities are now probing Routh’s background. The detainee is believed to have ties to North Carolina and Hawaii, sources said. Sources told ABC News that the FBI is conducting an extensive investigation into Routh’s social media activity, travel and any criminal record. Friends, family and associates are also being sought for interviews.

The suspect’s family is telling investigators that while Routh had no diagnosed mental illness, he “fixated” on things, multiple sources briefed on the investigation told ABC News.

An avenue of investigation is whether Routh became fixated on Trump over the former president’s stance on Ukraine. Routh appears to have made recent social media posts critical of Trump and used social media to document his travel to Ukraine.

According to the sources, Trump was getting ready to putt on the fifth hole when a Secret Service agent called out “gun!” Agents immediately surrounded Trump and took him to a predetermined secure location at the property. USSS often has these safe areas designated in advance.

Sources familiar with the investigation said authorities are looking into whether Routh had grievances related to Trump’s position on Ukraine.

Authorities are expected to file charges relating to the incident in the coming days, sources told ABC News.

President Joe Biden and Vice President Kamala Harris both condemned the apparent assassination effort.

“As I have said many times, there is no place for political violence or for any violence ever in our country, and I have directed my team to continue to ensure that Secret Service has every resource, capability and protective measure necessary to ensure the former President’s continued safety,” Biden said in a statement.

Harris said she was “thankful” that Trump was safe and “deeply disturbed by the possible assassination attempt.”

“As we gather the facts, I will be clear: I condemn political violence. We all must do our part to ensure that this incident does not lead to more violence,” Harris said.

On Monday morning, Biden said he believes the Secret Service needs more help and called on Congress to act following the second apparent attempted assassination attempt on Donald Trump in nine weeks.

“Thank God the president is OK,” Biden said before boarding Marine One to depart the White House. “One thing I want to make clear: The service needs more help. And I think the Congress should respond to their needs if they, in fact, need more servicemen, and so that’s what we’re going to be talking about.”

Asked what kind of help he thought the Secret Service needs, Biden said, “They’re deciding whether they need more personnel or not.”

CNN contributed to this report.