Did FBI chief James Comey bury Hillary Clinton's White House hopes?

Which Republican is most likely to impede Hillary Clinton's race to the White House? Most would say Donald Trump, but FBI director James Comey could be the surprise obstacle on her path to 1600 Pennsylvania Avenue.

Comey, a former federal prosecutor and ex-deputy attorney general, on Tuesday offered a damning assessment of her email practices during her time at the State Department -- but did not recommend she face criminal charges.

In an explosive -- and surprise -- 15-minute speech, the towering Comey -- he stands 6'8" (two meters) tall -- gave Clinton a dressing down that is sure to reverberate until voters head to the polls in November to choose President Barack Obama's successor.

He reiterated those views before a congressional committee on Thursday, facing a grilling over his impartiality but remaining unflappable under pressure, and insisting the FBI's conclusions were sound.

Of course, by saying Clinton was not criminally liable, Comey did not deal a death blow to her White House hopes. But the former first lady now will face difficult questions on the campaign trail for months until election day on November 8.

It will not be easy to erase the words uttered by Comey about Clinton -- his labeling of her as "extremely careless" will certainly be used in countless Trump attack ads.

Some experts even suggest the fallout could haunt her all the way to the Oval Office if she wins the presidency.

Comey said while there was no firm evidence that Clinton's email was successfully hacked, he also said he could not rule it out, and that sophisticated cyber criminals would not have left any trace.

On Thursday, he said Clinton "should have known not to send classified information." He also blasted the State Department as having a lax security culture under her leadership.

Only time will tell how Comey's words will affect Clinton's drive for the presidency.

- Straight shooter -

Comey, who has been in his position at the Federal Bureau of Investigation since September 2013, stole the spotlight from Attorney General Loretta Lynch, who could only announce Wednesday that she was following his recommendations.

Lynch sparked controversy last week when she met Clinton's husband, former president Bill Clinton, on the tarmac at the Phoenix airport -- a chat that left Republicans crying foul.

The year-long probe and its unusual conclusion have reinforced the view of Comey as a straight shooter, ready to take the heat from all sides in sticky situations.

Democrats are mad at how he painted Clinton in his assessment, and surprised at how much details he offered in a process that is usually kept secret.

Republicans are angry that she will not be charged, saying it defies logic given the errors that were made.

But Comey is a smooth operator with tons of experience in government.

- Connected -

For three decades, Comey has circulated in political and legal circles at the highest level, giving him the confidence to sometimes anger the country's justice department, and even the White House.

In the wake of the 2014 fatal police shooting of unarmed black teen Michael Brown in Ferguson, Missouri, Comey raised hackles by supporting cops who were wary of fulfilling their duties, for fear of their actions being caught on video.

Many top US government careers begin in New York, and Comey is no exception -- he hails from the Manhattan suburbs. He cut his teeth as a federal prosecutor in New York and the Washington area.

In 2003, he became deputy attorney general.

The following year, he faced one of his toughest showdowns, cementing his reputation for being independent and unafraid.

Comey had become acting attorney general due to the illness of his boss John Ashcroft.

At Ashcroft's bedside, the presidential counsel to George W. Bush, Alberto Gonzales, was trying to persuade him to reauthorize a controversial warrantless eavesdropping program.

Comey -- who was against extending the program -- later revealed the incident to senators, unleashing a political firestorm.