Less information leaves U.S. vulnerable as midterms approach

But people inside or close to the Kremlin remain critical to divining whether there is a strategy behind seemingly scattershot efforts to undermine American institutions.

Spies and informants overseas also give American intelligence agencies early warning about influence campaigns, interference operations or other attempts to compromise the United States. 

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At an appearance this month at the White House, Mr. Coats said intelligence agencies “continue to see a pervasive messaging campaign by Russia to try and weaken and divide the United States.” He added that those efforts “cover issues relevant to the elections.”

But officials said there has been no concrete intelligence pointing to Mr. Putin ordering his own intelligence units to wade into the election to push for a certain outcome, beyond a broad chaos campaign to undermine faith in American democracy. Intelligence agencies do not believe Mr. Putin has changed his strategy; instead, officials believe they simply do not have the same level of access to information from the Kremlin’s inner circle.

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“It is essential to have sources coming from inside the government. It was during the Cold War and it is today,” [Seth G.] Jones, who leads the transnational threats project at the Center for Strategic and International Studies, said. “There are multiple ways to collect intelligence against your adversary, in this case the Russian government. But sources can provide you things you might not otherwise get, like documents, intelligence assessments.”

Sources can provide photographs of Russian documents and intelligence that are hard to intercept electronically, and that can help the United States figure out what Russia is targeting, not just with its election meddling but with its attempts to infiltrate financial systems, the power grid and other critical infrastructure, Mr. Jones said.

The full reasons the sources have gone silent are not known. But current and former officials also said the exposure of sources inside the United States has also complicated matters.

This year, the identity of an F.B.I. informant, Stefan Halper, became public after House lawmakers sought information on him and the White House allowed the information to be shared.

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…. [S]ome allies have cited the exposure of the informant and other intelligence leaks in curbing some of the intelligence they share. And former spies believe that, long-term, the exposure will hurt overseas collection.

“Publicizing sources is really bad for the business,” [John] Sipher, [a 28-year veteran of the C.I.A. who served in Moscow in the 1990s and later ran the agency’s Russia program,] said. “The only thing we can offer people is that we will do anything in our power to protect them. And anything that wears away at that trust, hurts.”