DENVER, Colo. — Senate Majority Leader Harry Reid's scathing attacks on everything from Mitt Romney’s personal integrity to his devotion to his faith won't be going away for one simple reason, people close to the Democrat say: Reid personally, deeply loathes Mitt Romney.

Reid, a fellow Mormon and one-time boxer who has never been known as much of an orator, has emerged unexpectedly this year as the Democrats' most effective attack dog, doing particular damage to Romney with questions and innuendo about his personal tax returns. With the election approaching fast, the Nevada senator seems to be looking for new excuses to throw a right hook.

“Reid is doing all this on his own," said a source close to the Democratic leader. "This is his instinct at work combined with his distaste for Romney whom he thinks lacks any foundational principles or spine, and appears to feel entitled to gentler-than-normal treatment. Reid thinks that if you're going to get in the ring you should be ready to take some punches."

On one level, Reid’s crusade against Romney is simply “Harry being Harry,” as longtime confidants, aides, and observers are wont to say of the prickly yet soft-spoken Democrat.

To the casual observers — the ones who even know his name — the low-profile Reid is generally viewed as a mumbly, somewhat dull grandpa figure who often rambles at length about his hometown of Searchlight, Nevada. But those who have done battle with him in the Beltway know all too well not to trust his aw-shucks public persona: First and foremost, he is a dirty inside fighter.

Listen closely to Reid’s hometown nostalgia trips, and you’ll hear about the making of a gritty, combative fighter, winning boxing matches, crusading against the Mob in Las Vegas, and taking care of a mom who supported their family by cleaning the clothes of prostitutes.

The distance Reid has traveled from his hardscrabble upbringing is almost immaterial — he still holds his childhood in reverence, and he’s allowed it to shape the way he practices politics. Consequently, even the political opponents who detest Reid, and there are many, begrudgingly concede his abilities in trench warfare.

But according to those close to Reid, his open hostility toward Romney is much more than normal Harry Reid as political pugilist: It’s also a clear reflection of his contempt for Romney as a politician.

“Harry doesn’t respect Romney at all,” said a source familiar with Reid’s decision to go on the attack against the Republican nominee.

Although much has been made throughout his career about his penchant for incendiary statements, Reid usually reserves them for enemies he has for whom he has little respect.

For instance, the Senate Majority Leader long viewed George W. Bush as a weak opponent, and as a result he heaped scorn on him for years, famously calling the former president a “liar” at one point during his second term in office.

Reid’s counterpart in the Senate, Minority Leader Mitch McConnell, on the other hand has never felt Reid’s sharpest barbs, despite an often-acrimonious professional relationship in which both men have sought to make the other a boogeyman. Likewise, even as he waged intense ideological warfare with House Speaker John Boehner, he never unleashed the types of personal insults he has against Romney.

That difference in treatment is a direct result of Reid’s respect for McConnell and Boehner, those familiar with the Nevada Democrat acknowledge privately. It is only when Reid finds himself sparring with someone he views as below him, as he does with Romney, that the truly brutal aspects of his political persona begin to show themselves.

Reid’s no-holds-barred attack on Romney’s religious life last month was instructive, both in its intensity, and in Reid’s capacity to go after Romney in a way that no other Democrat can.

While Democrats across the country were piling on Romney after the leaked 47% fundraiser video, Reid went for the jugular in a conference call with reporters. He told them Romney had “sullied” their faith, and insisted, “he is not the face of Mormonism.” The remarks were met with criticism from both outraged Republicans and skittish Democrats who didn’t want to be associated with anti-Mormonism.

“I thought that was way, way out of bounds,” Rep. Jason Chaffetz, a Utah Republican and Mormon, told BuzzFeed. “You can criticize Mitt Romney for a lot of things, but to attack him on his religion I thought was uncalled for and unfounded. Unfortunately, Senator Reid has a reputation of making unfounded attacks.”

Reid defiantly stood his ground. He recognized that, as a Latter-day Saint, he was unencumbered by the potential of being cast as an anti-Mormon, said Jim Manley, a former top aide in Reid’s leadership office.

“Reid’s a good, committed Mormon, his faith is very important to him and he takes it very seriously,” Manley told BuzzFeed. That, in turn, gives him the ability to raise “an issue few have brought up during this campaign election.”

But Manley also said the religious digs went deeper than political opportunism, and reflected Reid’s genuinely dim view of Romney’s fealty to Mormon teachings about compassion and taking care of the needy.

Reid’s ideological differences with Romney represent deeper fault lines that run through American Mormonism. While the vast majority of U.S. Mormons are politically conservative, the church also contains a small but growing group of progressives, many of whom take defiant delight in parking their Obama bumper-stickered mini-vans in their church parking lots. Reid is a sort of folk hero to these types of liberal Latter-day Saints, and has long used his position to argue that Democrats have an important place in the faith.

In keeping with his very public mingling of faith and politics, Reid bristles at the notion that Mormonism should somehow be off limits in this race, Manley said.

“[For Reid] it’s no different than raising how Ayn Rand, for instance, relates to Catholic teachings,” Manley said. “The fact is you can’t square Ayn Rand with the Gospel of Christ.”

Manley also noted that Reid has worked with Catholic Bishops in opposing Ryan’s budget because of its cuts to programs aiding the poor.

“He sees a similar analogy with Romney and the Mormon faith,” Manley said.

On Thursday, Utah Sen. Orrin Hatch used a speech at the Colorado CPAC to predict a desperate Obama campaign would turn their firepower at Romney’s faith.

"They're going to get frustrated and clutched —and when I say they I mean the Obama people — and before the end of this race they're going to be so clutched that they're going to start attacking Mitt Romney's religious feelings," Hatch said. "And let me tell you something, get prepared for it."

But while it remains unlikely that anyone in Chicago will order an assault on Mormonism — the last untouchable part of the Republican’s personal life — Reid will keep taking jabs at Romney, wherever he senses weakness.

“Senator Reid doesn’t care” who he makes uncomfortable, Manley said. “He’s not afraid of controversy.”

He added, “He’s a plain-spoken individual… Yes, he sometimes says things others are afraid to say, but many people believe. “