Timothy Egan on American politics and life, as seen from the West.

In barely a century’s time, the population of the United States has more than tripled, to 313 million. We are a clattering, opinionated cluster of nearly all the world’s races and religions, and many of its languages, under one flag.

You would not know any of this looking at who is voting in one of the strangest presidential primary campaigns in history. There is no other way to put this without resorting to demographic bluntness: the small fraction of Americans who are trying to pick the Republican nominee are old, white, uniformly Christian and unrepresentative of the nation at large.

None of that is a surprise. But when you look at the numbers, it’s stunning how little this Republican primary electorate resembles the rest of the United States. They are much closer to the population of 1890 than of 2012.

Given the level of media attention, we know an election of great significance is happening on the Republican side. But it’s occurring in a different place, guided by talk-radio extremists and religious zealots, with only a vague resemblance to the states where it has taken place. From this small world have emerged a host of nutty, retrograde positions, unpopular with the vast American majority.

But before getting into how this minority has steered the party into a corner, let’s look at the size of the electorate. The nine states that have held caucuses or primaries to date are home to roughly 28 million total registered voters, of all political persuasions.

So far, three million voters have participated in the Republican races, less than the population of Connecticut. This means that 89 percent of all registered voters in those states have not participated in what is, from a horse-race perspective, a very tight contest.

Yes, we know Republicans don’t like their choices; it’s a meh primary. But still, in some states, this election could be happening in a ghost town. Less than 1 percent of registered voters turned out for Maine’s caucus. In Nevada, where Republican turnout was down 25 percent from 2008, only 3 percent of total registered voters participated.

This is not majority rule by any measure; it barely qualifies as participatory democracy.

Results from the two populous states that have held big, media-saturated primaries, and are more likely to attract average voters, are also very revealing. In Florida, the largest and most diverse state among the nine, turnout was down 14 percent from 2008. And 84 percent of the state’s total registered voters did not participate in the Republican contest.

South Carolina is the major outlier this year, the only state to show a big increase in turnout, up 35 percent from 2008. But when you look at who voted, you see a very specific niche.

In the Palmetto State, 98 percent of primary voters were white, 72 percent were age 45 or older and nearly two-thirds were evangelical Christian, according to exit polls. From this picture, you may think South Carolina is an all-white, aging state, full of fervent churchgoers. But the Census says the state is only 66 percent white, with a median age of 36. Exit polls from 2008 put the evangelical vote at 40 percent of total.

Florida was at least closer — only in the Latino vote — to the general election of 2008; in both cases, it was about 14 percent of the total. But voters 45 or older made up 78 percent of the primary, versus 59 percent in the general matchup four years ago.

Outside of Florida, this contest has been nearly an all-white affair. Nevada is 26 percent Latino by population; in the primary, only 5 percent were Latino. Caucus voters in Iowa were 99 percent white.

Again, these numbers represent a small echo chamber. Whites are 63.7 percent of the total population of the United States; in 1900, they were 88 percent — still more diverse than Republican primary voters today.

The takeaway point of this poorly attended, unrepresentative Republican primary contest is not to focus entirely on who is voting but on why the candidates are taking such fringe positions. One explains the other.

Thus, the New York Times poll of this week found that all voters, by a 66 to 26 ratio, support the federal requirement that private health care plans cover the full cost of birth control for female patients. Among women, support is 72-20. And with Catholics, it’s 67-25. Yes, Catholics are slightly more liberal than the population at large.

Other polls show a huge majority of Americans want to raise taxes on the rich, favor the planned withdrawal from Afghanistan and believe the earth is warming because of human action.

Yet the Republican front-runner of the moment, Rick Santorum, is with the minority on each of these issues, and Mitt Romney is a near match.

So, given how out of sync these two candidate are with the rest of the country, how could they be the front-runners? It’s simple: Look at who is voting, a nation unto itself.