David Stockman has spent so much time on TV these past few months, from 60 Minutes to Colbert, that he could be mistaken for a Kardashian. The story line is always the same: Ronald Reagan’s former budget director believes that extending Bush-era tax cuts is irresponsible. He also has plenty of harsh words for President Obama and the Democrats, but television producers are suckers for genuine Republicans who oppose Republican orthodoxy. So welcome back, David Stockman.

Why now? Stockman says he was “stunned and appalled” by the Wall Street bailout, which “in essence repudiated the entire Reagan revolution.” Plus, he’s working on a new book. Okay, that works. But after all these years, should we even care what he thinks? Well, if you take a close look at his investment activities over the past 25 years, maybe not.

Stockman left politics in 1985, eventually joining the Blackstone Group (BX) as one of its earliest partners. Despite some early successes, he became known internally for hyping bad deals and arguing against investments championed by others. “Stockman’s Cassandra act soon wore thin, not only because it put him at loggerheads with his partners but because he often was just wrong,” said David Carey and John Morris in their history of Blackstone, King of Capital. Blackstone ultimately decided to move Stockman into a role with less dealmaking responsibilities, which the former OMB director took as his cue to leave. In 1999, Stockman formed Heartland Industrial Partners, a new private equity firm that raised $1.3 billion to invest behind his belief in a coming Rustbelt revival.

The results weren’t pretty. (In fact, the only saving grace is that Heartland failed to raise the $2 billion it originally sought.) Canada Pension Plan, one of Heartland’s investors, said its $145.9 million investment was valued at just $45 million as of June 30, 2010. Research firm Preqin has data showing that Heartland’s returns worked out to just 34¢ on the dollar, compared with a median of $1.77 for other U.S.-based buyout funds of a similar vintage. Underwhelming, to put it generously.

The worst of Heartland’s concentrated portfolio was Collins & Aikman, an auto parts maker in which Stockman had invested while at Blackstone via what people in the private equity world call a “buy and strip.” Once the deal began to sour, Stockman installed himself as CEO. Things only got worse from there, with Stockman resigning just days ahead of a Chapter 11 bankruptcy filing in 2005. Two years later federal prosecutors alleged that Stockman had knowingly misled investors about the company’s pre-bankruptcy health. Criminal charges were later dropped, but this past spring Stockman settled with the SEC for $7.2 million.

Stockman still maintains his total innocence — telling WSJ.com last month that the SEC is “a money-harvesting machine” and that his decision to settle was one of convenience. Whether or not you believe Stockman, at least one thing is not in dispute: His original investment thesis was inherently flawed. Stockman blames the Collins & Aikman collapse on wider U.S. auto industry troubles, as if they were some catastrophic event that had been impossible to predict. Kind of tough to swallow, considering that the entire concept of a Rustbelt revival was predicated on overcoming existing difficulties. Sure, things might rebound, but was it really inconceivable to think that proven problems could become more severe?

Stockman told me his private-sector record has no bearing on his current pronouncements, including that the Obama/McConnell tax cut compromise is a “Keynesian flimflam.” “I’m commenting on the principles of public policy and how they’ve been betrayed,” he said. “I don’t know how that’s relevant to the rate of return on my investments.”

The relevance, of course, is that Stockman spent the past 25 years betting billions on macroeconomic trends that rarely panned out. Yeah, a long track record of being wrong doesn’t necessarily disqualify Stockman from a career in punditry (see: Morris, Dick, and an army of others). But at the very least somebody ought to mention Stockman’s past before asking him about the future.