Sorrow for the family of Kathryn Steinle is appropriate. So is anger at her killer and all those in the chain of causation that led to her murder.

But her slaying by an oft-deported illegal immigrant felon should not prompt Republican presidential candidates to become amplifiers for that small slice of the electorate which sincerely believes illegal immigration is the most pressing issue facing the country.

This is a trap into which some candidates will fall. But the Iranian nuclear program, the Islamic State, the People's Republic of China and Vladimir Putin must all be greater priorities for the next president than control of the southern border — even though that control is also an element of the nation's security.

The Republican Party has been cautious about which journalists will be asking questions in debates and framing the issues of the GOP primary. But the anti-illegal immigration absolutists, who brand every immigration reform proposal as "amnesty," distort that primary as surely as a debate panel of Media Matters propagandists ever could. There is no upside in generalizing about all immigrants (even all illegal ones) from this murder, or from the legion of "sanctuary cities." And there is considerable political downside to it as well.

There is also the question of consistency. If states may now simply go their own way on dope laws, why shouldn't cities legislate their own immigration policies? After all, both are flouting specific federal laws and the Supremacy Clause of the Constitution. To run a "rule of law" campaign will oblige every candidate to consistently demand that rule in every case. If a candidate finds an applause line for a condemnation of sanctuary cities, they should be willing to then condemn marijuana sanctuaries as well, or at least explain why the two categories of law-breakers are different.

Target "sanctuary cities," and the GOP will be branded anti-immigrant. And spare me the "I'm for legal immigration but against illegal immigration" line — of course they are different subjects, but tens of millions of voting U.S. citizen listeners to Spanish language media will not hear that distinction. They will instead hear "Vote for Hillary."

GOP candidates will soon attempt to distinguish themselves on the key basis of which one is best suited to defeat former Secretary of State Hillary Clinton. She, in turn, would like nothing more than for 16 would-be GOP nominees to focus on the worst few thousand illegal immigrants out of a population of millions, turning attention away from the slowly unfolding results of her own foreign policy failures in Iran, Iraq, and elsewhere.

Message discipline right now — in the face of a horrific outrage and a genuine legislative problem — will demonstrate an ability to remain focused for the 15 short months ahead. This week and the weeks before the debates begin will show separation in the field — not in poll numbers, but in seriousness about winning the general election. Watch very closely for the steadiness that a nominee will need in making the case against Hillary, no matter what the headlines bring.

Hugh Hewitt is a nationally syndicated talk radio host, law professor at Chapman University's Fowler School of Law, and author, most recently of The Queen: The Epic Ambition of Hillary and the Coming of a Second "Clinton Era." He posts daily at HughHewitt.com and is on Twitter @hughhewitt.