Reid's Mormonism is unthreatening. America does not fear excessive religious zeal in its Democrats, as it tends not to worry about weakness on security from its Republicans. It would be counterintuitive. In any case, the job of Senate minority leader is a backroom task for a political engineer. It does not hold sway over the Union.
But a Mormon running as a Republican for the presidency is another matter. Americans want their presidents not just to represent them, but also to embody them somehow as a nation.
Would a Mormon be permitted to do that?
The precedents are not favourable. Joseph Smith, the founding prophet of the Latter-day Saints church, declared his presidential candidacy in 1844, at a time when his followers were a community of outcasts in Illinois. In July that year, he was shot dead by an anti-Mormon at the age of 38, before his campaign even got going. His successor, Brigham Young, fled west to Utah with the remaining Saints (including Miles Park Romney, Mitt Romney's great-great-grandfather).
They took with them Smith's prophecy that one day a Mormon would come to America's rescue.
Mormons would be "the staff upon which the nation shall lean", the prophet predicted, when the constitution "is on the brink of ruin". The next man to try to fulfil that prophecy was Mitt Romney's father, George, an automobile executive and a three-term Republican governor of Michigan who was born in a polygamous Mormon community in Mexico. He launched an ill-fated presidential campaign in 1967, but proved too gaffe-prone even to last until the official starting post, the New Hampshire primary.
In 2000, it was the turn of Orrin Hatch, a softly spoken Republican senator from Utah, but his campaign was quickly crushed under the Bush steamroller. Before Hatch's effort collapsed, a survey found that 17% of Americans would not vote for a Mormon president under any circumstances.
"One reason I ran was to knock down the prejudicial wall that exists," Hatch later told the Weekly Standard. "I wanted to make it easier for the next candidate of my faith."
That candidate is Romney, who insists that the diehard opposition to Mormonism accounts for only a few per cent of the electorate. That may be optimistic on his part. Elections, especially presidential elections, act like a giant magnifying glass on a candidate's weak points, and Romney's chief weakness will be Mormon history and dogma.
The press will want to know, for example, whether he wears the Mormon's secret and sacred undergarments beneath his politician's suit. There will be a fresh look at why the Latterday Saints' priesthood was closed to black people until 1978, and whether its principal text, the Book of Mormon, is inherently racist. Evangelical conservatives, the backbone of the Republican party, will quiz him on his faith.
Many deny that it is Christian at all. "The challenge to governor Romney would be the most serious in the Republican primaries," said John Green, an expert at the Pew Forum on Religion and Politics. "Many of the evangelicals take a dim view of the Latter-day Saints. The Southern Baptists regularly label the Mormons as a dangerous cult. So you could imagine his opponents might bring this up."
Although Christ is a central figure in Mormon beliefs, the church teaches that God has a material body, and was fathered by another God. Joseph Smith also said that man can ultimately ascend to heaven and become "what God is": divine. Yet despite - or perhaps because of - these fundamental differences from established Christian dogma, the church is a powerful and growing force. It claims 12 million adherents around the world, two-thirds of them in the US, where it is one of the fastest-growing religions.
That's a lot of potential campaign volunteers. The Church of Christ of Latter-day Saints is, after all, the only truly American mass religion. It places the Garden of Eden in Jackson County, Missouri, and claims Christ visited America after the resurrection to promise his second coming, also in Missouri. It is an entirely home-grown faith. Joseph Smith founded the religion in 1830 in upstate New York, telling his followers an angel had appeared to him and handed him the Book of Mormon in the form of gold tablets.
Smith gave the tablets back after translating them from the original "reformed Egyptian". According to the Book of Mormon, Israelites came to the American continent 600 years before Christ, but split into two feuding tribes, Nephites and Lamanites. The Nephites were "pure" (the word was "white" in Mormon scriptures until 1981) and led by a great man called Mormon. Lamanites were idol-worshipping and wicked, and therefore suffered the "curse of blackness" that turned their skins dark. The Lamanites eventually wiped out the Nephites, which is why Christopher Columbus found only brown-skinned native Americans when he arrived. All these Mormon tenets will come under unprecedented scrutiny in a presidential race, which will be an uncomfortable time for the apostles in Salt Lake City.
The difference between a cult and a religion may only be a couple of thousand years, but while the origins of mainstream Christian faiths have acquired the blurred patina of age, the Mormon scriptures are jarringly recent and, in many cases, patently wrong. DNA testing, for example, has shown that the first Americans arrived from Asia, not from the Middle East.
But no Mormon doctrine or practice has proved more troubling to the church than polygamy. The principle did not form part of Smith's original scriptures, but came to him as a revelation years later. He is said to have taken a second wife, a 16-year-old housemaid, in 1833 - and 30 more wives over the next decade, to the disgust of some of his disciples.
The legacy endured for nearly half a century after Smith's death, and the church only surrendered it as a compromise, in return for Utah statehood. Polygamy has dogged Mormonism ever since, and it will dog Mitt Romney's bid to become the Latter-day Saints' first president.
The fact is that polygamy makes lousy politics - for all the same reasons it will no doubt make great television.