One of the best things about President Bush is the way he has avoided his father’s errors. He has done so, from the beginning of his first presidential campaign, in a way that lets America know that while he respects and honors his father, he is his own man. Where 41 stopped short of Baghdad and left Saddam Hussein in power, 43 finished the job. Where 41 raised taxes in the face of hand wringing about deficits, 43 has been a tax cutter, facing down some of the harshest, and most demagogic, ridicule over his commitment to the idea that raising taxes on the top margin, or just on the wealthy, is not the way to provide incentives for economic growth.

Until now. In what is one of the major blunders of his presidency, Mr. Bush, in a little-noticed interview with reporters for regional newspapers, left open the door to a huge increase in the payroll tax as part of his Social Security “reform.” Heretofore Mr. Bush’s position has been to rule out any increase in the payroll tax. But in the interview, Mr. Bush made clear that while he rules out an increase in the payroll tax rate, he was open to an increase in the pay roll tax base. The tax now applies only to the first $90,000 an individual earns. But whether it’s the rate or the base, make no mistake, it’s a tax increase, and a big one.

Here’s how the New Haven Register, which participated in the session, reported it: “Asked whether he would oppose Social Security taxes on income over the current limit of $90,000, Bush left the matter open. ‘I’m interested in good ideas. People need to come forth with good ideas. The one thing I won’t do is negotiate with myself,’ Bush said.” The Register story also noted that Senator Grassley, the Republican who chairs the powerful Finance Committee, said Sunday he expected any Social Security overhaul would apply the payroll tax to income above $90,000.

This is a faulty idea for so many reasons that it is hard to know exactly where to start, but begin with the politics of it. After an election campaign in which Mr. Bush said in the second presidential debate, “I’m not going to run up taxes, which will cost this economy jobs,” for the president to go ahead and approve what amounts to a massive tax increase on those who earn more than $90,000 a year would be a tremendous breach of faith. For years to come, it would discredit Republican candidates who campaign on the hard-won high-ground of promises of tax cuts.

It would blur the distinction between tax-cutting Republicans and tax-raising Democrats. In the third presidential debate, Mr. Bush said of Senator Kerry, “He voted to increase taxes 98 times,” and said, “the way to make sure our economy grows is not to raise taxes on small-business owners. It’s not to increase the scope of the federal government. It’s to make sure we have fiscal sanity and keep taxes low.” You don’t have to be Karl Rove to realize that turning around after that and signing a massive tax increase would be seen by a lot of voters as a genuine betrayal.

It’s not just the politics that are bad news here, but the economics. Raising this tax would be, for many of the most productive Americans, a marginal tax increase of precisely the kind that causes people to work less, and makes the entire American economy less productive. Americans for Tax Reform, the advocacy group run by one of Mr. Bush’s allies, Grover Norquist, calls it “terrible tax policy.” Americans for Tax Reform notes that under such a plan, “a family making $110,000 per year would face a 20% increase in total federal taxes, wiping out most of President Bush’s tax cuts.”

The group warns that “substantially raising the marginal tax rate will reduce the incentives to work, save, and invest, which reduces the amount of revenue collected.” As it is, the phase-out of the payroll tax takes some of the sting out of the progressive rate structure of the federal income tax, making the system as a whole flatter and so less punitive on the most economically productive Americans.

If the rich are going to have to pay the freight for Social Security “reform,” we’d rather see it happen by cutting their guaranteed benefits than by increasing their taxes. The benefit-cutting approach makes government smaller, while the tax raising approach makes government bigger. The best approach of all would be to grow the pie so that neither tax increases nor benefit cuts are necessary. We can understand Mr. Bush’s instinct to let Congress work out the details on this. But if Mr. Bush isn’t careful, the details will include a tax increase. And as the president’s father found out, the one who gets blamed for that is the man – and the party – in the White House.