Iowa has two Senators, one a Republican (Charles Grassley), the other a Democrat (Tom Harkin).

Each has voted seven times since 2002 on a bill to raise the nation's debt ceiling. Look back at those votes, and an interesting pattern emerges: Every time a Republican president has needed the debt ceiling raised to keep government functioning, Sen. Grassley, the Republican, has voted to raise it, while the Democrat, Sen. Harkin, has voted against it. But when a Democratic president has asked for an increase, their votes reverse: Sen. Harkin has voted in favor, and Sen. Grassley has voted against it.

That, in a nutshell, shows why it's so absurd that Washington is headed toward a showdown over debt and the deficit tied to the question of whether to raise the national debt ceiling. Few exercises produce as much cynical and overtly partisan behavior by elected officials as do votes on the debt ceiling.

When the party in power needs the debt ceiling raised, its representatives in Congress do what they must to let the government pay its bills and keep the full faith and credit of the U.S. in order. Meanwhile, the opposition party gives posturing speeches about the evils of debt. When power changes hands, the roles reverse. In all cases, lawmakers are voting to limit debt they help create in the first place.

The debt ceiling is, in short, a deeply flawed vehicle for an important conversation. Yet it is the vehicle that will be used. The U.S. government will hit its current debt ceiling of $14.3 trillion in mid-May and, technically, lose its ability to borrow. By using accounting tricks, the Treasury could put off default until July 8, at which point the government would be unable to pay creditors. The financial markets would convulse.