Liz Sullivan, left, and Jim Steinle, right, parents of Kathryn Steinle. (Lea Suzuki/San Francisco Chronicle via Associated Press)

From the start, Fox News host Bill O’Reilly has been transparent about his response to the killing of Kate Steinle in San Francisco earlier this month, a crime allegedly committed by Juan Francisco Lopez-Sanchez, an undocumented immigrant who’d been deported five times. “I have departed from my usual analytical job and become an advocate to keep criminal aliens out of the country,” said O’Reilly in his broadcast last Thursday night.

The border-protection scheme can be spotted on BillOReilly.com: “Pass Kate’s Law ASAP,” a petition effort that the host is promoting on Fox News. This legal change would declare that “undocumented aliens who are deported and return to the United States would receive a mandatory five year sentence in a federal penitentiary upon conviction.” It’s addressed to Senate Majority Leader Mitch McConnell (R-Ky.) and House Speaker John Boehner (R-Ohio). As of last night, there were about 400,000 signatures on the site, O’Reilly reported on his program.

How would O’Reilly’s petition change the status quo? It depends on the circumstances. The basic punishment for reentry after deportation is a fine and a prison sentence not exceeding two years, or both. If deportation follows a conviction for an “aggravated felony,” however, the maximum prison sentence is 20 years.

Whereas the existing statutes allow sentencing discretion, “Kate’s Law” would not: “The key word is ‘mandatory’ — no wiggle room,” said O’Reilly of his initiative on last night’s “O’Reilly Factor,” in which he conducted a compelling interview with Jim Steinle and Liz Sullivan, Kate Steinle’s parents. To appreciate how the law is applied to contemporary cases, consider:

* A Canadian man in April was sentenced to two years in federal prison for illegally reentering the United States. He had previous felony convictions, including for armed robbery and felony petty theft.

* An MS-13 gang member was sentenced to 30 months in prison for illegal reentry after having been removed from the United States and deported to El Salvador in 2007, and again in 2011. In 2005, he was convicted in Los Angeles of second-degree robbery.

* A Mexican man received a 21-month sentence in March for illegal re-entry.

As for the man charged with Steinle’s killing: Lopez-Sanchez had been deported five times and notched up seven felony convictions. As the New York Times said with great understatement, that record raised “questions about why he was in the United States.” This Los Angeles Times story details Lopez-Sanchez’s tour through the U.S. immigration and criminal justice systems.

Addressees on O’Reilly’s petition drive aren’t yet assessing the idea on its merits. “This horrific crime highlighted a serious problem in our immigration and enforcement system,” notes Emily Schillinger, press secretary for Boehner, in an e-mail to the Erik Wemple Blog. “The Speaker supports efforts to address the issue, and the chairmen and members are reviewing potential options.” Don Stewart, a spokesman for McConnell, wrote via e-mail, “There’s certainly a good deal of interest in this issue. The Judiciary Committee has a hearing next week where this will undoubtedly be a focal point.”

Petitioning Congress for a legal change sets a theme of coverage for autumn editions of “The O’Reilly Factor.” “I think what we would like to do is bring you both to Washington to talk to the congressmen and the senators who are putting the law together,” said O’Reilly to Steinle and Sullivan last night. “They go on vacation in August. I think when they come back we will get you both to Washington to talk to them face to face. Maybe to testify in front of some committees there so you can have input and we will report every step of the way,” said O’Reilly, promising that “it will be at our expense.”

With that, O’Reilly moves from analyst to activist-cum-lobbyist, seeking help from politicians to prevent a recurrence of the Steinle tragedy. No debate can be entertained about the worthiness of the cause, yet O’Reilly takes up issues all the time that he views as critical to “the folks” and for which he stops short of petition drives. Bernard Goldberg, a forceful regular presence on “The O’Reilly Factor,” last week pronounced “Kate’s Law” a reasonable extension of O’Reilly’s franchise: “Bill, this is an opinion show. It’s not a hard news show. It’s not the CBS Evening News, and I think what you did, by advocating for that law was well within the boundaries of opinion journalism.”

Those boundaries are in the eye of the commentator. At the very least, hoisting a petition up the marble steps of Capitol Hill subjects a guy like O’Reilly to all kinds of program-slanting conflicts. Will he give preferential coverage to lawmakers who back his idea, or penalize those who oppose it? Will he make behind-the-scenes calls to rally support, or will everything be aired on “The O’Reilly Factor”? And if Congress somehow passes the change and it handcuffs judges and strains the budget of the federal prison system, will O’Reilly report it all? Just asking.