A deal struck by Congress and the White House to raise the debt ceiling doesn't solve the country's long-term fiscal imbalances and merely delays a fiscal crisis that will return and threaten the economy, Erskine B. Bowles and Alan K. Simpson, co-chairmen of the National Commission on Fiscal Responsibility and Reform.

The deal calls for at least $2.1 trillion in deficit reduction, including caps on discretionary spending worth around $900 billion in savings over 10 years, in exchange for lifting the country's $14.3 trillion debt ceiling and avoid default.

The plan, Simpson and Bowles say, is a good start but doesn't go far enough.

Erskine Bowles (L) and Alan Simpson (R) (Getty Images photo)

"This country needs a plan to reduce our deficits by no less than $4 trillion in the next decade," the two write in a New York Times op-ed piece.

"It needs a plan to cut more wasteful spending in the defense and nondefense budgets than this deal does. In addition, we must address the unsustainable growth of our entitlement programs and reform the tax code to make it more competitive and more efficient."

Simpson, a Republican, and Bowles, a Democrat, say "big-ticket items" such as Social Security, Medicare and Medicaid will need reform if the country is to avoid bankruptcy.

President Barack Obama himself has said the deficit reduction plan approved by Congress in exchange for lifting the debt ceiling is a first start and adds that more work must be done to right the country's debt-ridden economy.

"It's an important first step to ensuring that as a nation we live within our means," Obama says, according to the Associated Press.

"This is, however, just the first step. This compromise requires that both parties work together on a larger plan to cut the deficit."