What the April 2018 US sanctions on Russian firms signalled
An analysis of the sanctions package announced under the Countering America's Adversaries Through Sanctions Act, and what its stated grounds covered.

What did Washington say it was targeting when it sanctioned Russian companies in the days before 10 April 2018? According to reports from 6 April 2018, the United States imposed sanctions on twelve Russian-owned companies, a Russian arms exporter and a bank, using the Countering America's Adversaries Through Sanctions Act.
The legal basis matters. The act, known as CAATSA, is a US federal law that imposed sanctions on Iran, North Korea and Russia by preventing US companies from doing business with sanctioned entities. The Senate passed it on 27 July 2017 by 98 votes to 2, after the House approved it by 419 to 3. President Donald Trump signed it into law on 2 August 2017, though he believed the legislation was "seriously flawed".
The stated grounds were broad. The US cited Russian meddling in the 2016 elections and military engagements in Ukraine, Crimea and Syria, among other reasons. For Ukraine, the notable point is that its conflict with Russia appeared on that list alongside other grievances, rather than as the sole justification.
The package combined three kinds of target: ordinary companies, an arms exporter and a bank. That mix meant the measures reached both commercial and defence-related business, and the financial sector. Beyond that, the reports from the period describe the designations and the reasons given, not their economic effect, which would have to be judged from later evidence.