It’s hard to pinpoint exactly when Rick Santorum suddenly ceased to be the viable challenger and began instead to be a candidate in denial. Wisconsin is, as Andrew Malcolm put it, Santorum’s “next last chance” and it doesn’t look good for the former Pennsylvania senator. Maryland and D.C., where Santorum didn’t even make the ballot, have never been anything but Romney territory.

The weeks ahead don’t look any more promising for Santorum:

So, we enter a three-week window after today’s action with the volume likely growing from those who care, asking why Ricky doesn’t just give it up. It’s hard, given how determined, committed and focused these candidates must be for so many long days so far from home, to give up emotionally, even though the math is as clear as a sweater vest.

Next on April 24, come five primaries — Connecticut (28), Delaware (17), New York (95), Pennsylvania (72) and Rhode Island (19). Romney’s coming on in Pennsylvania and looks good elsewhere. Santorum regards his home state as a last bastion. But the most recent time he ran there (2006), he lost by an historic 18 points. So, it could also be an Alamo.

The ex-senator says he’s in the fight until Romney gets the necessary 1,144, which is what a stubborn Mike Huckabee said about John McCain’s lead four years ago. And now Huck is playing bass guitar Saturdays on the Fox News Channel.

Santorum says he represents the GOP’s base, which is true if you consider the base is only Very Conservative evangelicals. All of the other parts — Somewhat Conservative evangelicals, women, college educated, suburbanites, et al — have come around to Romney.

Yet, his campaign continues to wage the valiant messaging battle. Spokesman Hogan Gidley today, for example, sought to explain Santorum’s inevitable D.C. loss as the result of something other than the campaign’s own organizational oversight.

“Obviously Wisconsin is going to be a close race, we’re not sure about Maryland or Washington, D.C.,” Gidley said Tuesday on MSNBC. “We expect Mitt Romney to do well in the D.C., area, no shock there, in fact it might even be unanimous — I don’t know that we’ll pick up a single vote in D.C. because of the vitriol D.C. has for a someone like Rick Santorum who wants to shake things up here in Washington.”

Santorum, for his part, has outright said he doesn’t want to answer the dreaded question: Will he exit the race anytime soon?

“I’m not talking about this anymore,” Rick Santorum said [in West Bend, Wis.] Sunday outside the Riverside Brewery and Restaurant before a gaggle of cameras and reporters. “We’re just focused on doing well here in Wisconsin.”

What Santorum doesn’t want to talk about is what so many others want to talk about, which is how long he will stay in the contest for the Republican presidential nomination. He is confronted by that question at almost every stop along the campaign trail and in every television interview he gives. He’s tired of it.

“I think I’ve answered the question I’m going to answer,” he says.

He’s earned the right to continue in the race, to compete in his home state of Pennsylvania, to explore every last avenue that might lead to the nomination. As improbable as it has been from the beginning, it is still not impossible.

No matter what happens, though, his campaign has been — for those of us who’ve watched and identified with someone who admittedly looks to his faith first and to his political ideology second — an inspiration. His heartfelt determination, his unprompted speeches, his outspoken opinions, his shining family — they’ve reminded us that authenticity is always relevant and that no one gets anywhere worth going by attempting to be something other than who and what he is. Rick Santorum has been — from the first day of his campaign to this — Rick Santorum. In politics, a field in which strategists recreate candidates in the image of electability, that might just be the most impressive feat of all.