There has been no news on NASA's commitment to the ExoMars mission, pending the release of the President's FY13 budget proposal next month. That budget will also determine how funding for the Webb Space Telescope will impact NASA's planetary program.
Several recent articles have discussed how difficult it will be to fund new flagship missions. While the emphasis is on astronomy missions, the same issues likely will apply to flagship planetary missions. I recommend Big science in an era of tight budgets.
Editorial Thoughts: The impacts of the continuing financial downturn are still being felt. NASA's budget proposal to be released next month will be the first to follow the release of the Decadal Survey and the commitment to the higher funding needed to complete the James Webb Space Telescope. If the Decadal Survey laid out a vision, then the next budget will be the administration's response to that vision and the other competing priorities for NASA in an era of budget cutting. The administration has promised to include its decision on NASA's participation in the ExoMars as part of that budget release. I plan to release an analysis of the budget proposal the day it is released.
From the Space News article, it appears that the next opportunity to revisit ESA's commitments will come at the ministerial meeting next November.