HOUSE MAJORITY Leader Eric Cantor (R-Va.) on Thursday pulled out of bipartisan talks on raising the debt ceiling, followed swiftly by his Senate counterpart, Republican Jon Kyl of Arizona. Republicans claimed their continued attendance was pointless because of Democratic insistence that tax revenue be part of any broad budget deal. This behavior is childish and irresponsible. It risks disaster — in the short term because of the anxiety it could create over the prospect of U.S. default, and in the long term because new revenue and spending cuts both must be part of any reasonable approach to controlling the spiraling national debt.

“There is not support in the House for a tax increase, and I don’t believe now is the time to raise taxes in light of our current economic situation,” Mr. Cantor said in a statement. The first part of his explanation demonstrates his failure of leadership. The second misstates what the negotiations are about. The fundamental argument is not over tax increases now, at a point when the recovery is disturbingly fragile. It is about raising revenue over a period of years, along with, and at a far lower amount than, massive spending cuts.

Senate Republicans were no more tethered to reality. “The White House and Democrats are insisting on job-killing tax hikes and new spending,” Senate Minority Leader Mitch McConnell (R-Ky.) said in a statement with Mr. Kyl. “That proposal won’t address our fiscal crisis, our jobs crisis, or protect and reform entitlements. . . . President Obama needs to decide between his goal of higher taxes, or a bipartisan plan to address our deficit. He can’t have both.”

Spare us the rhetoric about job-killing tax hikes. Any look at the job-creating records of President Bill Clinton (who raised taxes) and President George W. Bush (who slashed them) should put that canard to rest. Moreover, as Mr. Cantor acknowledged, Democrats have expressed a willingness to accept about $2 trillion in spending cuts over the next decade, going after both discretionary spending and entitlement programs. No one in the budget talks is proposing tax increases of that magnitude. Republicans are resisting any package that would raise net tax revenue — even by closing loopholes. Where is the Republican flexibility?

Which brings us to Sen. Tom Coburn. The conservative Oklahoma Republican, after bravely signing onto the relatively balanced package crafted by the president’s fiscal responsibility commission, had been part of the Senate’s bipartisan Gang of Six working to translate that framework into legislative reality. He has taken a leave of absence from the group. Now is the moment for him to return. Mr. Coburn’s conservative bona fides are unassailable. His renewed participation would give necessary comfort to other Republicans who understand that tax revenue must be part of the ultimate agreement but have been unwilling, unlike Mr. Coburn, to say so publicly. Whatever the disagreements that led him to leave the gang, they cannot be so serious as to outweigh the urgency of action.

“The problem is too big for us to take pot shots at each other on what we think is a political point. And we need to get down to the real business of having a plan that gets this country out of the very real difficulties we face. The very fact that we do not know when the problem is coming, the very fact that we cannot control our own destiny unless we start taking action now should give us all chills,” Mr. Coburn said on the Senate floor. That was last December. This is late June, and the debt ceiling is fast approaching. This could be Mr. Coburn’s moment to be the grown-up his party seems to be missing. If not him, then who? If not now, what will happen?