WASHINGTON – After weeks of arguing constitutional fine points and citing rival statistics, senators wrangling over gun control saw and heard the anguish of a bereft father.

Neil Heslin, whose 6-year-old son, Jesse, was among those cut down at Sandy Hook Elementary School in December, asked the Senate Judiciary Committee on Wednesday to ban assault weapons like the one that killed his child.

“I’m not here for the sympathy or the pat on the back,” Heslin, a 50-year-old construction worker, told the senators, weeping openly during much of his hushed 11-minute testimony. “I’m here to speak up for my son.”

At his side were photos: of his son as a baby, of them both taken on Father’s Day, six months before Jesse was among 20 first-graders and six administrators killed in the Newtown, Conn., school. That massacre has hoisted gun control to a primary political issue this year, though the outcome remains uncertain.

The hearing’s focus was legislation by Sen. Dianne Feinstein, D-Calif., to ban assault weapons and ammunition magazines carrying more than 10 rounds. A Bushmaster assault weapon was used at Newtown by Adam Lanza, whose body was found with 30-round magazines.

Feinstein said such a firearm “tears peoples’ bodies apart. I don’t know why … we can’t say they don’t belong.”

Republicans argued her proposal would violate the Second Amendment and that current gun laws are not fully enforced.

“The best way to prevent crazy people” from getting firearms is to better enforce the existing federal background check system, said Sen. Lindsey Graham, R-S.C.

That system is designed to prevent criminals, people with mental problems and others from obtaining guns. It only applies to weapons sold by federally licensed dealers, and expanding that system to nearly all gun transactions is the central proposal in President Obama’s package of gun restrictions he unveiled last month, along with bans on assault weapons and large-capacity magazines.

As if to underscore the hurdles Obama’s plan faces, House Judiciary Committee Chairman Bob Goodlatte, R-Va., said he opposed universal background checks like Obama wants and predicted it would not be part of his chamber’s gun legislation. He wants the current federal background check system strengthened, improving how states provide it with mental health information about citizens and cracking down on illegal gun trafficking.

The Senate Judiciary panel could begin writing gun legislation Thursday, but that seems all but certain to slip to next week.

At the Senate hearing, spectators wept as Heslin described his last morning with his son, including getting a final hug. The hearing room was packed with relatives and neighbors of victims of Newtown, as well as people affected by other shootings at Aurora, Colo., and Virginia Tech.

Dr. William Begg, who treated some Newtown casualties, described assault weapons wounds.

“They had such horrific injuries to their little bodies,” said Begg. He said an assault weapons bullet “opens up” and does not travel in a straight line, adding, “That’s not a survivable injury.”