Space News has an article (Russia Withholding Plutonium NASA Needs for Deep Space Exploration) stating that Russia is withholding promised plutonium-238 for NASA missions. This follows Congress' decision not to start the process for new production of plutonium-238 in the United States for the current fiscal year. According to the article, Russia wants to negotiate a new contract, but no reason is given. (It may be that the Russians realize that without U.S. production capabilities, NASA can be forced to pay considerably more for plutonium than the current contract calls for.)
The article goes on to state that the Jupiter Europa Orbiter cannot be flown without (1) the Russian plutonium, (2) a restart of U.S. production, or (3) use of the unproven ASRG power sources. Either of the latter two cases would slip launch of the mission past 2020.
The article states, "Jim Green, NASA’s director of planetary science, recently told scientists drafting the U.S. space agency’s next 10-year plan for robotic exploration of the solar system that the era of plutonium-powered missions could be coming to an end."
Bad news indeed.