Correction: An earlier version of this editorial incorrectly said that Congress had repealed the alternative minimum tax. In its year-end budget agreement, Congress permanently indexed the tax for inflation. The following version has been updated.

FORMER SENATOR Alan Simpson (R-Wyo.) and former Clinton White House chief of staff Erskine Bowles administered a dose of realism to Washington on Tuesday, announcing an update to their eponymous 2010 deficit-reduction plan. This new Simpson-Bowles outline seeks $2.4 trillion in ten-year savings, on top of the $2.7 trillion already achieved — thus potentially bringing the ratio of debt-to-gross domestic product below 70 percent by early next decade and putting it on a downward path thereafter.

This is $900 billion more debt reduction than President Obama advocated in his State of the Union address. Good: Mr. Obama’s goal is not ambitious enough. It would leave debt-to-GDP at a dangerously high 73 percent by 2023, with no plan to prevent it from rising after that. Simpson-Bowles 2.0 would take some steps Mr. Obama has already contemplated — such as adjusting federal tax brackets and benefits by a more realistic inflation measure — as well as some he would not — such as going above $400 billion in health-program savings over 10 years.

But there’s almost no point debating the specifics, because there’s little chance of a “grand bargain” along Simpson-Bowles lines. Mr. Obama and his Republican opponents can’t even agree on how to avoid a short-term across-the-board spending cut — “the sequester.”

The sequester would slash $85 billion between now and Sept. 30, half from discretionary programs and half from defense. Both of these have already been trimmed in previous budget deals — defense to the point where Pentagon leaders predict damage to national security if the sequester goes through on March 1. Entitlements, meanwhile, remain unreformed.

Yet neither party has staked out anything like a serious negotiating position. Last year, the GOP-led House passed a bill to replace the defense sequester with cuts to funding for Obamacare insurance exchanges, nutrition aid, social service grants and other Democratic favorites. Since then, the Republicans have agreed to postpone the sequester for two months as part of the year-end “fiscal cliff” avoidance deal, but otherwise they seem to have concluded that allowing the sequester is in their political interest. Even ill-advised spending cuts are more base-pleasing than none, apparently.

The Senate Democratic majority has suggested eliminating the sequester by, among other things, cutting farm subsidies, closing certain high-profile tax loopholes and imposing a 30 percent minimum tax on individual income above $1 million per year. This is one big non-starter: Members of both parties want farm subsidies and loophole-closing to pay for other planned reforms, and the millionaire’s tax, though base-pleasing for Democrats, amounts to bringing back the alternative minimum tax.

Meanwhile, Mr. Obama seems content to warn of dire cutbacks in everything from naval operations to firefighters and to accuse the GOP of risking them to protect the wealthy. The Republicans denounce the sequester as Mr. Obama’s brainchild (though they accepted it as part of a 2011 budget deal) and say they won’t vote for any more tax increases. Both sides are obviously playing a political blame game, which must give way to serious bargaining soon — or the country will be the loser.