Former White House chief of staff Erskine Bowles and former senator Alan Simpson (R-Wyo.), co-chairmen of President Obama's fiscal reform commission, kicked off a campaign Tuesday to promote the panel's final report and the efforts of a group of senators working on long-term deficit reduction.

The leaders of the National Commission on Fiscal Responsibility and Reform testified Tuesday morning before the Senate Budget Committee about the report, which recommends measures to cut annual deficits by $4 trillion by 2020.

On Tuesday afternoon, the two were slated to join with the bipartisan "Gang of Six" senators to launch the "Moment of Truth Project," a program sponsored by the New America Foundation.

The events come as the Senate and House continue to wrangle over how to keep the government funded through the end of September. Simpson, Bowles and the senators' group are working to turn attention back to the country's longer-term fiscal issues.

At the outset of Tuesday’s Senate Budget Committee hearing, Bowles acknowledged that the commission’s report was “a politically very, very difficult plan to support,” but emphasized that the country’s long-term deficit problem is “the most predictable economic crisis in history.”

“A lot of us sitting in this room didn't see this last crisis as it came upon us,” he said. “But this one is really easy to see. The fiscal path we are on today is simply not sustainable.”

Both he and Simpson were peppered with questions from senators on the ins and outs of the committee report as well as President Obama’s proposed budget for fiscal 2012. The two repeatedly emphasized the need to restore the solvency of Social Security; Simpson pushed back against claims that they’re “balancing the budget on the backs of poor, old Social Security people.”

“That's a fake, it's a phony, it's wrong, it's untrue,” he said.

Simpson added that if Congress can’t get Social Security solvent for 75 years, “you can forget everything. You will never get to Medicare, Medicaid and defense. You will have failed what we see as the easiest thing to do, which is to restore the solvency of Social Security for 75 years.”

Both acknowledged that Obama’s fiscal 2012 proposal fell short of what they would have liked to have seen. Bowles said that Obama’s budget “does a relatively good job” of dealing with domestic discretionary spending cuts but doesn’t make cuts to defense spending or other types of reforms that the commission would like to have seen.

This post has been updated since it was first published.