With the accession of a Democratic majority in Congress, we knew to be on guard for tax increases. We just didn’t think we needed to be watching out for the Heritage Foundation, a mainstream conservative think tank in Washington, where, when we last visited, a portrait of Ronald Reagan was hanging in the lobby.

At issue is a fix to Social Security. President Bush tried for private accounts as part of the program in 2005 but failed to get a Republican Congress to approve the idea. Part of Mr. Bush’s problem was that he focused on solvency. He sounded like an actuary or an accountant instead of a visionary politician who believed in empowering Americans to own their own retirement accounts instead of relying on a government program with a shaky future and poor returns.

Now the prospect of a Social Security fix has reappeared in Washington. It could give Mr. Bush a domestic legacy accomplishment to exit his presidency with, and it could give Democrats in Congress the chance to claim they had tackled a tough problem. It could also give Democrats the opportunity to protect their presidential candidates from having to deal with the issue in a general election campaign in 2008, in which their opposition to private accounts would be a political loser.

How does Heritage enter the picture? The think tank has been on a campaign against the rising costs of federal entitlement programs, which are indeed alarming. And when we rang a senior research fellow at Heritage, David John, he said that he was, as part of a comprehensive overhaul of Social Security, “willing to look at” lifting the cap on the amount of earnings that are subject to the 12.4% Social Security tax. That cap has been creeping up, in nominal terms, on its own — in 2005, an employee’s first $90,000 in wages were subject to the tax, in 2006, $94,200. In 2007,$97,500 in wages will be subject to the tax.

Some Democrats propose increasing the tax rate of 12.4%. But increasing the tax base — the amount of income subject to the tax — is just as much of a tax increase as increasing the base. Mr. John has written in the past against a lifting of the cap and opposes any Social Security overhaul in which a lifting of the cap is the only adjustment to the program. But that only makes his refusal to rule out a tax increase all the more disappointing, and surprising. He makes the point that in order to fix the problem, everyone is going to have to compromise.

Now, one telephone conversation isn’t a policy decision by Heritage, which has a long record of great wisdom on tax matters. But the kind of statements Mr. John has made recently have low-tax activists in Washington privately expressing concern. The key point is that if Republicans go into the negotiations favoring a tax increase, you can bet that what comes out after the Democrats get their hands on it is going to be an even bigger tax increase.

Mr. Bush has been a heroic tax cutter, which is one reason the stock market is soaring and unemployment is low. If the cost of Social Security “reform” is a tax increase, Mr. Bush may decide that the economic expansion is legacy enough. If the Heritage Foundation wants to team up with a president on a 12.4% marginal tax increase, Mr. Bush may figure, let it be Hillary Clinton.