Rep. Darrell Issa likes to show visitors to his office a bullet-riddled body-armor plate that was manufactured in his district.

He holds up a new model that offers better protection for soldiers, but cautions that even the latest prototypes have limits.

"Ultimately, these things are not bulletproof," Issa said as he examined a shield. "When you are getting riveted, you've got to get out of there. You don't stand there like one of those movie stars, taking bullets in the chest forever."

It's a fitting metaphor for Issa, Republican chairman of the House Oversight and Government Reform Committee, whose aggressive style of taking on government agencies, most recently the Internal Revenue Service, has drawn a barrage of hit pieces in the news media.

Some of the attacks, which delved into his arrests for alleged car thefts as a youth, were purportedly orchestrated by the White House press office, according to Mark Leibovich in his new book, "This Town," about the self-absorbed Washington media.

Despite the unrelenting criticism, Issa isn't running for cover. And he hasn't been knocked down yet.

He's plowing ahead as the top watchdog in Congress, overseeing a Democratic administration and its agencies, and he's got the enthusiastic encouragement of top GOP leaders to keep digging for dirt.

On July 18, Issa will preside over his second hearing into the IRS practice of targeting conservative groups seeking federal tax-exempt status.

The hearing, he said, will disprove the Democrats' contention that a few misguided employees in the agency's Cincinnati office were behind the decision to scrutinize conservative groups.

"We are going to close that chapter," Issa said.

The hearing, and others to follow, will build the case that the targeting is directly linked to Washington, Issa said.

"What did the people in Cincinnati do?" Issa plans to ask two key IRS officials at the hearing. "What was their role and how did they view the people they were interfacing with in Washington?"

Issa's investigation of the IRS targeting has contributed to a drop in President Obama's popularity. According to one recent poll, people believe by a margin of 48 percent to 38 percent that senior White House officials called for the targeting, though Issa admits there is no direct evidence connecting it to Obama aides.

He plans to keep looking, however.

"How high does it go?" Issa asked rhetorically in an interview with the Washington Examiner. "We are going to go through in ascendancy order to see who wants to take the blame, or tell us why they are not responsible in spite of the fact that their hands were on this wrongdoing."

Because the IRS has a major role in implementing Obamacare, Issa's probe has helped the GOP revive its effort to repeal or scale back the massive health plan.

Issa, a self-made millionaire who represents a San Diego district, has brought national attention to the agency's targeting of 500 conservative groups that applied for 501(c)(4) tax-exempt status between 2010 and 2012.

The House Ways and Means Committee and Senate panels have also held hearings on the IRS. But Issa's inquiries have gotten the most attention, both positive and negative, because of his brash style and tough questions.

One of his Democratic predecessors, Rep. Henry Waxman, a California Democrat, accuses Issa of "throwing political spitballs." But Issa's GOP colleagues think his approach is just fine.

"Darrell is a confident chairman without concern for the hue and cry of the media or the talk shows," Rep. Patrick McHenry, R-N.C., an oversight panel member, told the Examiner. "He's very willing to engage in the big fights and is unafraid."

It was Issa's request for an internal investigation by Treasury Inspector General J. Russell George that set the scandal in motion. George reported that IRS agents devised a system to "Be On the Look Out" for certain groups with conservative-sounding names including the words "Tea Party" and "Patriot." His report found that conservative applicants were subjected to intrusive scrutiny and months-long delays not experienced by liberal organizations that applied for tax-exempt status.

Issa's hearing on the targeting highlighted the IRS admission that agents leaked confidential information about Republican presidential candidate Mitt Romney's donation to the National Organization for Marriage. The IRS gave the information to the Human Rights Campaign, an LGBT advocacy group that publicized it in the spring of 2012 with the aim of making Romney appear opposed to gay rights.

Weeks after the agency's targeting was revealed, Issa held a hearing on a report showing that the IRS had spent nearly $50 million between 2010 and 2012 on lavish employee conferences that included a "happiness expert" and expenditures of tens of thousands of dollars for speakers to discuss such topics as "Leadership Through Art."

The investigation comes as the agency prepares to play a central role in administering and enforcing the health insurance mandate, which is supposed to provide much of the funding for Obamacare.

Republicans are seizing on the Obama administration's recent decision to delay implementation of the employer mandate to push their attempt to block the law.

"The IRS is hardly the most beloved institution in the country and I don't think people even realized the IRS was involved in Obamacare," said Mike Tanner, a senior fellow at the libertarian Cato Institute. "This investigation has pointed that out, and it doesn't engender a lot of warm, fuzzy feelings."

House Republicans plan to vote soon on a bill sponsored by Rep. Tom Price, R-Ga., that would block the IRS from enforcing or implementing any part of the health care law. Price, citing the IRS investigation, said the agency is "clearly unable to prudently and impartially enforce current law" and should not be involved in Obamacare.

Republican leaders also announced legislation that would slash IRS funding by $3 billion, a quarter of its budget, a move that would significantly hinder the agency's ability to oversee Obamacare.

When he unveiled the bill, House Majority Leader Eric Cantor, R-Va., referred to "a growing sense of distrust of what this administration and what Washington is doing."

Issa's IRS investigation has continued despite intense pressure from Democrats to back down. They argue that liberal groups were also targeted but that Issa simply narrowed the investigation so that conservatives appear to be the only victims.

Democrats point to the recent disclosure by IRS watchdog J. Russell George that the agency also flagged liberal groups that applied for tax-exempt status.

"I think the initial Republican narrative is in a shambles," Rep. Gerry Connolly, a top Democrat on the House oversight panel, told the Examiner.

Connolly pointed out that George was appointed by President George W. Bush and once served as a Republican staffer on the oversight panel.

George was told by Issa to only investigate conservative targeting, Connolly argued, and he subsequently withheld evidence from the committee that showed liberal groups were also targeted.

"It would be nice if there were an acknowledgement on the other side that their outlandish claims, without any foundation in fact whatsoever, were wrong," Connolly said. "I don't see the other side doing that. I see them doubling down."

Issa disputes Connolly's claim.

George, he said, acknowledged that liberal groups were flagged, but they were not subjected to the same relentless inquiries and endless foot-dragging experienced by conservative groups.

"There has been no statement of delay, denial of due process or abusive questioning by any progressive group," Issa said.

Issa and Connolly agree on one point: The oversight chairman is ramping up his investigation.

He will raise the issue of the agency's trustworthiness and competency to administer the health care law at another hearing that will be run by Rep. James Lankford, R-Okla., one of Issa's subcommittee chairmen. The hearing, Issa said, will focus on "the ability or inability of the IRS to ensure the American people of their privacy with this very confidential information."

As for the bombardment of negative press, Issa shrugs it off. He pointed to a painting on his office wall of President Andrew Jackson, whose wife was accused of adultery and bigamy by the press because of a glitch in obtaining a divorce from her first husband.

Jackson believed it drove his wife to an early death, Issa said, but that won't happen this time.

"If you can't take being personally attacked for what you do on policy, then you can't live in Washington," Issa said. "That is just part of life here."