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.

Republicans and some Democrats—correctly sensing that it's time for the federal government to take seriously its need to break its debt addiction—have decided to take a stand on the debt ceiling: no increase without some serious moves to cut deficit spending.

It's an understandable impulse and a threat the Obama administration takes seriously. Vice President Joe Biden will convene a select group of House and Senate leaders starting on May 5 to come up with what the administration calls a framework for reducing the deficit, in hopes that will be enough to persuade lawmakers to vote to raise the debt ceiling.

The problem is that even those leading this process have little idea what this framework is supposed to contain or how real it has to be. Both sides say Congress is playing with fire with the debt ceiling. Worse, it is playing with an instrument that has long produced more partisan grandstanding than honest debate.

One notable recent grandstander was President Barack Obama, the man who now badly wants the debt ceiling raised to prevent financial disaster. When he was a Democratic senator and Republican George W. Bush was president, Mr. Obama took to the Senate floor to declare that raising the debt ceiling amounted to "leadership failure," and he voted against it. The White House says he now considers that vote a mistake.

But the president has company. Senate Republican leader Mitch McConnell voted to raise the debt ceiling six straight times when Mr. Bush was in the White House. But he has voted "no" both times a vote has come under Mr. Obama.

Donald Marron, an economist at the Tax Policy Center, has compiled figures showing just how partisan debt-ceiling votes are. In the House of Representatives, there have been three up-or-down votes in the last decade in which the vote was 100% partisan—that is, it passed solely with the votes of the president's party.

In the Senate, the pattern is similar. When Mr. Obama needed a debt-ceiling increase in 2009 and 2010, he got one Republican vote the first time (from the now-retired Sen. George Voinovich of Ohio) and no Republican votes the second time. Similarly, when Mr. Bush needed debt-ceiling increases in 2003, 2004 and 2006, he got three, two and zero Democratic votes, respectively.

Here's a notable exception: In 2002 and 2007, when power was divided between the parties, some bipartisanship emerged, at least in the Senate. In 2002, for instance, a debt-ceiling increase passed the House with 212 Republican votes and only three Democratic, but in the Senate the split was 31 Republican and 37 Democratic.

So it's possible for divided government, which Washington has again, to produce bipartisan behavior, which is what the country needs on deficits. Unfortunately, only rarely does the debt ceiling call forth such mature behavior.

Write to Gerald F. Seib at