RUTHFULLY YOURS

This is a crucial thread tying Russia to the attack, not that you’d know it from the media and political chatter. Russia’s defenders have seized on the statement by Gary Aitkenhead, head of the Porton Down military lab, that “we have not identified the precise source” of the chemical. Labour Leader Jeremy Corbyn mocked Foreign Secretary Boris Johnson for saying last month that the lab had confirmed the chemical was Russian. Diane Abbott, one of Mr. Corbyn’s deputies in Parliament, claimed Labour’s “more thoughtful approach” to Salisbury had been vindicated.

That spin is at best disingenuous. Although the molecules don’t have “Made in Russia” stamps on them, Porton Down has confirmed the chemical is Novichok, which is known to be produced in Russia and nowhere else. The lab says it required “extremely sophisticated methods to create, something only in the capabilities of a state actor,” as Mr. Aitkenhead told Sky News. He was clear that his conclusion is only one piece of evidence to be evaluated.

This finding bolsters Prime Minister Theresa May’s case that Vladimir Putin’s government is responsible for the first use of a chemical weapon on European soil since World War II. Other evidence includes intelligence that Russia has experimented with chemical agents for assassinations and previously targeted former Russian agents—including Alexander Litvinenko, poisoned with radioactive polonium in London in 2006.

Mr. Putin would love nothing better than for Western politicians to fall into the rabbit hole of playing molecular “CSI” while ignoring other evidence of Russian culpability. That’s one reason the Kremlin has staged such histrionics at the Organization for the Prohibition of Chemical Weapons in the Hague, calling for a special session this week to discuss Salisbury and demanding a joint Russian-British investigation to distract from the group’s work on the case.

Voters should be asking why politicians such as Mr. Corbyn are so eager to apologize for Mr. Putin. The war of words over the Porton Down analysis comes at an especially sensitive time, since Britain is debating additional responses to the attack.

Financial sanctions belong at the top of the list. A parliamentary committee is looking at ways to limit Russian financial activity in Britain, perhaps blocking Russian government bond sales in London. Home Secretary Amber Rudd has said her office may re-evaluate some of the hundreds of visas issued to Russians under a program that allows anyone to move to Britain—with a path to eventual citizenship—in return for a £2 million investment in risk-free U.K. government bonds.

Any financial sanctions will be politically difficult to pass given the profits British banks, law firms, investment advisories and others earn serving wealthy Russians. And to truly bite, sanctions against individuals linked to Mr. Putin’s government would require international coordination. That coordination already is difficult in a European Union where pro-Kremlin states such as Greece and Hungary enjoy vetoes on EU foreign policy. False confusion about facts such as the Porton Down conclusions gives political cover to Mr. Putin’s enablers.

Mrs. May has won important diplomatic victories by patiently presenting evidence to allies and, as far as possible, to the public. One result was a show of solidarity from French, German and U.S. leaders. Another was last month’s mass expulsion of Russian spies from Western countries. The best way to keep up the pressure on Mr. Putin is to continue treating the Salisbury attack as the strategic threat it was, rather than as a plot in a “Law & Order” episode.