The ever nastier fight between former terrorism chief Richard Clarke and manifold Bush officials has taken on a “he said, she said” quality. It’s hard to know who to believe.

But having routinely undercut his credibility elsewhere, President George W. Bush should bear the burden of proof vis-a-vis Clarke.

While Clarke was making his case before the National Commission on Terrorist Attacks Upon the United States, Medicare’s chief actuary, Richard Foster, was telling the House Ways and Means Committee that he shared estimates of the burgeoning cost of the proposed Medicare drug bill with administration officials last summer. Yet former Medicare administrator Thomas Scully threatened to fire Foster if the latter released the estimates to Congress.

“We can’t let that get out,” Foster said Scully told him. Health and Human Services Secretary Tommy Thompson has reluctantly ordered an investigation, but that’s not nearly enough.

Scully has denied the charge, saying that his threat to fire Foster was made in jest. But Scully admits that he ordered Foster to stonewall Congress at one point because, Scully believed, Democrats would use the estimates for political advantage.

The political advantage of non-disclosure accrued to the administration, however: Foster warned that the legislation would cost an extra $100 billion to $200 billion over its first 10 years, an increase of between 25 percent and 50 percent. Had Congress learned the truth, legislators would have killed the proposal, which passed by just five votes.

Indeed, Republican conservatives, many of whom voted yea only under enormous administration pressure, were particularly insistent on limiting costs. “I think a lot of people probably would have reconsidered because we said the $400 billion was our top of the line,” explains Rep. Sue Myrick, R‑N.C.

Even so, only blatant intimidation allowed the GOP leadership to eke out a narrow victory. Then came the administration’s January admission, just weeks after the bill’s passage, that the legislation would cost at least one-third more than expected, $434 billion instead of $395 billion.

Although the GOP Congress voted in 1997 to prevent the Clinton administration from hindering legislators’ access to the Medicare actuary, Bush administration officials disclaimed any responsibility for alerting Congress to changing cost figures.

Last year, Scully said that the Medicare actuary worked for the executive branch and that he, Scully, would release cost estimates “if I feel like it.” Which he obviously didn’t.

Once the revised number emerged, Thompson said nothing: “I did not tell them because it was not my responsibility.” Apparently his only responsibility was winning votes by hoodwinking the people’s elected representatives. The president has said nothing about this scandal so far.

Equally serious is the weapons of mass destruction fiasco. The president, vice president, secretary of state and secretary of defense painted a veritable arsenal of horrors. Nuclear weapons programs, anthrax, biotoxins, chemical weapons, nerve agents, smallpox, biological weapons trailers, unmanned aerial vehicles, long-range ballistic missiles and more were being developed and deployed for use against America.

Said President Bush: “Intelligence gathered by this and other governments leaves no doubt that the Iraq regime continues to possess and conceal some of the most lethal weapons ever devised.” And this threat was direct, imminent, significant, urgent, gathering and mounting. Indeed, said Defense Secretary Donald Rumsfeld, “No terrorist state poses a greater or more immediate threat to the security of our people and the stability of the world.” Of course, none of these claims were true.

And administration officials had reason to know, or at least suspect, that many of them were false. Observed John B. Judis and Spencer Ackerman of the New Republic, “Unbeknownst to the public, the administration faced equally serious opposition within its own intelligence agencies.”

The CIA, Defense Intelligence Agency, Air Force, State Department’s intelligence bureau, Department of Energy, and International Atomic Energy Agency criticized various administration claims. The top-secret National Intelligence Estimate on Iraq included some 40 caveats, which were left out of the public version. Moreover, the United Nations inspectors actively traversing Iraq found nothing.

At no point has the president or his advisers accepted responsibility. At worst, they appear to be conscious liars. At best they seem deceitful and manipulative.

That doesn’t mean that Clarke is right and the administration is wrong. But it does mean people are understandably suspicious of administration excuses.

Indeed, it’s why President Bush’s trustworthiness ratings have fallen. The president and administration officials have no one to blame but themselves. Instead of attempting to trash Clarke’s reputation, the president should work to rehabilitate his own. A verbal acknowledgement of responsibility for past misstatements would be nice. Firing someone would be even better.

Trust, once squandered, is hard to regain. That is why the administration risks losing its high-stakes showdown with Clarke — and the election in November.