Eight former defense secretaries -- Democrats and Republicans alike, including Republicans who served Democratic presidents -- have written to congressional leaders urging passage of the Trans-Pacific Partnership on national security grounds.

TPP "is an important step in the process of furthering peace and increasing prosperity here in America and around the globe," they write. "The TPP will deepen relationships with allies in the Asia-Pacific region, strengthen the U.S. economy, establish high standards that mirror U.S. interests and values, and contribute to a safer world for ourselves, our children, and our grandchildren."

The trade deal between the United States and 11 other Pacific Rim countries was signed in February after years of negotiations. Congress may take it up this year, most likely in a lame-duck session after the November elections, but its passage is anything but assured.

The former defense secretaries single out "engagement and leadership in Asia" as "especially critical," calling the region the most important for American prosperity and security over the next century. "By 2030, two-thirds of the world's middle class -- more than 3 billion people -- will reside in Asia. This population not only represents a critical consumer base for Made-in-America exports, but an opportunity to strengthen alliances with regional powers such as Japan and Singapore," the letter states.

Then they get to the trade deal:

The TPP represents a choice for the United States. It is a choice between leading the world toward a future that supports U.S. values and interests, or standing back and allowing others -- most likely China -- to write the rules of the road for Asia in the 21st century. And let us be clear: trade rules written by China would not promote a trading system consistent with American interests and values. The United States cannot and should not fall behind on the world stage. Our leadership in a troubled world is dependent on our military, diplomatic, and economic power. We cannot afford to weaken any element of our strength at this critical time. With a trade agreement of this magnitude, there will be elements that some dislike, but the overall benefits to our economy and national security cannot be overstated. We urge you to support the TPP and to help the United States maintain its leadership in the 21st century.

Signatories include Chuck Hagel, Leon Panetta and Robert Gates, who served under President Obama (Gates also served under President George W. Bush); Donald Rumsfeld (Bush and Gerald Ford); William Cohen and William Perry (Bill Clinton); Frank Carlucci (Ronald Reagan); and Harold Brown (Jimmy Carter).