This is how a scandal implodes:

First, the head of the investigation overpromises. “This was a targeting of the president’s political enemies, effectively, and lies about it during the election year so that it wasn’t discovered until afterwards,” Rep. Darrell Issa (R-Calif.), chairman of the House oversight committee, said in May of the IRS targeting scandal. He later declared President Obama’s press secretary a “paid liar” for stating otherwise.

Next, facts emerge to undermine the investigator’s presuppositions. Documents released by Ways and Means committee Democrats this week show that the IRS, in addition to targeting tea party groups, also had “Be on the Lookout” (BOLO) lists for groups using descriptors such as “progressive,” “health care legislation,” “medical marijuana,” “paying national debt” and “green energy.”

Finally, evidence surfaces that the investigator stacked the deck. Tuesday night, the Hill newspaper quoted a spokesman for Treasury’s inspector general, Russell George, saying the group was asked by Issa “to narrowly focus on tea party organizations.” The inspectors knew there were other terms, but “that was outside the scope of our audit.”

Certainly, something went badly wrong at the IRS that caused groups to be targeted because of ideology. But it’s nothing like the conspiracy Issa cooked up in which the president and his men supposedly used the tax authority to attack their political foes.

The White House deserves some of the blame for letting things get this far; a full release of information by the administration at the outset would have put the controversy to rest quickly. But the collapse of the Issa-driven scandal has reinforced a growing impression in the capital that ultimately will help Obama: The chairman is full of it.

When I covered President Clinton’s second term, White House officials were delighted to have the eccentric Dan Burton in charge of the House oversight committee. He gained prominence by shooting a melon to try to prove that Clinton aide Vince Foster hadn’t killed himself but had been murdered.

Now Issa has fallen to Burtonian levels of credibility. He’s launched a dozen or so probes, but what often begins as a legitimate inquiry into government failure turns quickly into a lunge for the Oval Office, missing each time.

Even before the Republican victory in 2010 gave him the chairmanship, Issa announced the discovery of “Obama’s Watergate” — the White House floating an administration job for a Democratic congressman to keep him out of a Senate primary. Issa backed off after learning that the Bush administration had done similar things.

Shortly before the 2010 election, Issa told Rush Limbaugh that Obama “has been one of the most corrupt presidents in modern times.” He later said Obama isn’t “personally corrupt” but his administration is.

Issa then set out to prove it. He led a probe into the failed “Fast and Furious” gun sting by the Bureau of Alcohol, Tobacco, Firearms and Explosives. Issa declared that “it went all the way to the White House,” insisting that the plan was approved “at the highest levels of the Obama appointees,” and that the Justice Department “has blood on their hands.”

The Justice Department inspector general determined that Attorney General Eric Holder didn’t even know about the program until after it was shut down.

After the failure of Solyndra, a government-aided solar company, Issa probed Energy Department loan guarantees, saying “I want to see when the president and his cronies are picking winners and losers ... that it wasn’t because there were large contributions given to them.”

The committee documented no cronyism and no presidential involvement.

Issa probed the response to Freedom of Information Act requests by the Department of Homeland Security, saying the matter “reeks of a Nixonian enemies list, and this committee will not tolerate it.”

Nothing Nixonian surfaced.

After the killing of U.S. officials in Benghazi, Libya, Issa accused then-Secretary of State Hillary Clinton of giving false information to Congress when she said she wasn’t involved in denying the Libyan diplomats’ security requests. He also said that it was “perhaps the White House” that later changed talking points to make it appear that the assault had begun as a protest.

It turned out Clinton wasn’t involved in the security decision and the White House wasn’t behind the change in the talking points.

Then came the IRS. Instead of delivering on Issa’s promise to reveal politically motivated harassment of conservatives by the Obama administration, the committee instead turned up evidence (including the account of a “conservative Republican” who managed IRS screening) that the actions weren’t political.

The most Issa et al. can hope to prove now is that conservatives were hassled by the IRS more than liberals. That’s a worthy topic to explore, but it’s no Watergate.

Twitter: @Milbank

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