The problem is that—unlike the ready alternatives to Iranian oil—Europe has no way to replace Russian energy supplies. Russia supplies about 30 percent of the oil and natural gas imports that Europeans rely on to fill their gas tanks, heat and light their homes and run their factories. So cutting off the petro-Euros flowing back to Russia would inflict at least as much pain on Europe as it would on Russia.
Nor has the Russian government been shy about reminding Europeans where their energy comes from. Twice—during the depths of winter in 2006 and 2009—Russia shut off gas supplies to Ukraine over trade disputes, crimping supplies further west in Europe.
(Red more: White House's Russia investment advice)
Russia's militarized grab of Crimea further complicates negotiations over construction of a new gas pipeline that would bypass the Ukraine. The project, known as South Stream, was proposed by Gazprom, and rejected by European regulators in Dec. 2013. Those talks are likely to be much chillier follow the Russian annexation.
European leaders, meanwhile, are looking at a variety of alternatives to weaning their continent off Russian energy supplies over the long term.
One involves tapping the boom in U.S. oil and natural gas production, where pressure is building on the White House to speed permitting of export facilities for liquefied natural gas shipments. So far, only six such terminals have been approved. But even if fast-tracked, it would be years before enough additional terminals could be built to provide meaningful supplies to Europe.
(Read more: Europe 'hostage' by Russian nat gas: Hamm)
U.S. oil producers are also looking at exporting their expertise in hydraulic fracturing, or "fracking,"—the technology that sparked the boom in U.S. output. Several EU countries, including Britain, France, and Poland, are believed to contain enough undeveloped gas to supply about as much as a 10th of EU gas demand by 2035, according to the International Energy Agency.
"The powerful realities of infrastructure and gas economics will limit what Europe can ultimately achieve in this area, according to a report by IHS Global Insight. "Russia will remain a substantial gas supplier to Europe."
With Europe reliant Russian energy for years, if not decades, recent U.S. and EU threats of wider Russian sanctions appears limited to extending the list of wealthy Russians with offshore bank accounts.
—By CNBC's John Schoen. Follow him on Twitter
@johnwschoen or email him.