In early April, a 30-second television ad began airing in rural Pennsylvania close to where Vanguard, the giant asset manager, is headquartered. “When you save with Vanguard, you’re an owner of a catastrophic climate future,” the ad intoned. Sponsored by SOS, a network of civil-society organizations and financial experts, the ad criticized Vanguard for holding over $300 billion in the equities of fossil fuel companies.