WASHINGTON — Urging Americans to “do some soul searching,” President Barack Obama injected himself into the emotional debate over the fatal shooting of a teenager in Florida, turning the racially charged case into a personal matter for the nation’s first black president.

“If I had a son, he’d look like Trayvon,” Obama said Friday.

Obama’s words also catapulted the death in Florida of 17-year-old Trayvon Martin, already the focus of major national attention, into the presidential campaign. Three Republicans seeking Obama’s job all used the word “tragedy” to describe the shooting, as the president did.

“I can only imagine what these parents are going through, and when I think about this boy, I think about my own kids,” Obama said at the White House.

Obama said the parents of Martin, who was shot on Feb. 26 in Sanford, Fla., a suburb of Orlando, have a right to expect “that we’re going to get to the bottom of exactly what happened.”

Martin was shot by neighborhood watch volunteer George Zimmerman, who said he was acting in self-defense. Zimmerman’s father is white, and his mother is Hispanic. The shooting has stoked debate over race as well as other issues. Obama did not mention Zimmerman in his comments.

Republican presidential candidates quickly weighed in after Obama spoke.

Former Pennsylvania Sen. Rick Santorum called the shooting a “horrible case.” Referring to Florida’s “stand your ground” law, which gives people wide latitude to use deadly force rather than retreat during a fight, Santorum said: “Stand your ground is not doing what this man did.”

Former Massachusetts Gov. Mitt Romney said in a statement: “What happened to Trayvon Martin is a tragedy. There needs to be a thorough investigation that reassures the public that justice is carried out with impartiality and integrity.”

Former House Speaker Newt Gingrich of Georgia also called it a tragedy and credited local authorities for empaneling a grand jury. “There’s a point in there where there ought to be some kind of signal that’s pretty clear that this is a guy who’d found a hobby that’s very dangerous,” Gingrich said of Zimmerman.

Florida is a large and diverse state that plays an influential role in presidential elections _ it was a deciding factor in the 2000 election following a lengthy recount. The Orlando area in central Florida is particularly important, acting as a bellwether for statewide elections.

The case resonates with many black Americans, a key voting group during Obama’s 2008 election, who see it as an example of bias toward blacks. Civil rights groups have held rallies in Florida and New York, saying the shooting was unjustified. Of Sanford’s 53,000 residents, 57 percent are white and 30 percent are black.

Obama directed his message to Martin’s parents, saying, “I think they are right to expect that all of us as Americans take this with the seriousness that it deserves, and we’re going to get to the bottom of what happened.”

He said that “every parent in America should be able to understand why it is absolutely imperative that we investigate every aspect of this and everybody pulls together, federal state and local, to figure out exactly how this tragedy happened.”

The White House had said earlier in the week that it was “not going to wade into a local law enforcement matter” though offering sympathies for Martin’s family. But that changed when Obama answered a shouted question following a Rose Garden ceremony to announce the president’s choice to lead the World Bank.

Obama cautioned before speaking that he must “be careful so we’re not impairing any investigation.” But he said he was glad the Justice Department was investigating and that Florida officials had formed the task force.

“I think all of us have to do some soul searching to figure out how did something like this happen, and that means we examine the laws and the context for what happened as well as the specifics of the incident,” Obama said.

White House spokesman Jay Carney said later that the president “had thought about” the case and “was prepared to answer that question when he got it.”

Martin’s parents, Tracy Martin and Sybrina Fulton, thanked Obama for his support, saying in a statement the president’s words “touched us deeply and made us wonder: If his son looked like Trayvon and wore a hoodie, would he be suspicious, too?”

NAACP President Benjamin Jealous said in an interview that Obama “spoke from the heart of a parent and the experience of a parent of color, but also from the pulpit of our national leader. And we needed to hear all of those things in this moment.”

Obama, early in his term, also spoke out after the arrest of Henry Louis Gates Jr., a black Harvard University professor, by a white police sergeant in Cambridge, Mass.

Gates was arrested in his home after the police sergeant arrived to investigate a possible burglary. The charges were dropped, but Obama said the police had “acted stupidly.” The president said later he should have expressed his concerns with different language and invited both Gates and Sgt. James Crowley to the White House for a chat and a beer.

The Justice Department and FBI have opened a civil rights investigation into Martin’s death, and a grand jury is considering whether to charge Zimmerman. Martin’s parents, civil rights activists and others who have reacted to the case say they won’t be satisfied until Zimmerman is arrested.

Martin was returning from a trip to a convenience store when Zimmerman started following him, telling police dispatchers Martin looked suspicious. At some point, the two got into a fight, and Zimmerman pulled out his gun.

Zimmerman told police Martin attacked him after he had given up on chasing the teenager and was returning to his sport utility vehicle.

Police Chief Bill Lee stepped down temporarily this week to try to cool the building anger that his department had not arrested Zimmerman. Hours later, Gov. Rick Scott announced that the local state attorney, Norman Wolfinger, had recused himself from the case in hopes of “toning down the rhetoric” surrounding it.