The only place you’ll find happier people today is at the White House. Photo: Saul Loeb/AFP/Getty Images

Yesterday afternoon, as I was making my way into the White House for an interview, I ran into David Axelrod trundling along on his way out. We chatted idly for a few minutes about the political topic du jour: Who was Mitt Romney going to pick as his running mate? I told Axelrod that I was still convinced, as I had been for months, that Rob Portman would be the guy (ahem), and sagely explained why it wouldn’t be Tim Pawlenty (phew) and just couldn’t be Paul Ryan (doh!). Axelrod studiously maintained a poker face throughout our discussion. But I couldn’t help but detect a gleeful flicker in his eyes when we talked about the fervor on the right for the congressman from Wisconsin.

With Mitt Romney’s announcement this morning that he had tapped Ryan, the very same flicker is enlivening the eyes of everyone residing at the Obama for America HQ in Chicago and in the warrens of the White House, coupled with grins wide enough to span the distance between the two. But as giddy as Democrats are about the pick, so are Republicans and in particular conservative stalwarts. The underlying cause of the joy on both sides is the same, and it also happens to be the reason why the country should love the selection too: It raises the stakes and starkly clarifies the choice that voters will face in November — in one fell and dramatic swoop transforming a campaign that was teetering on the edge of being about nothing (of substance, that is) into a contest about Very Big Things indeed.

That the right is thrilled comes as no surprise, of course, given the despondency sinking in among hard-core conservatives (and, really, most Republicans) over the state of the Romney campaign during this long hot summer. Themeless, timid, error-prone, and on the defensive over Bain, taxes, and the dreadful foreign trip, the Romney campaign has seen their guy’s position in the race steadily erode, with three new polls showing him behind by seven to nine points and Obama at or near 50 percent (CNN 52-45 percent, Fox 49-40 percent, Reuters/Ipsos 49-42 percent). While the GOP political class has loudly and justifiably lamented Team Romney’s poor performance on defense against Team O’s attacks, conservatives have been more troubled by its abject failures of offense: its inability or unwillingness to lay out a bold and clear agenda to contrast with that of the president.

In choosing Ryan, Romney, in effect, both acknowledged and granted the validity of that latter set of criticisms. As my colleague Jonathan Chait and others have written, Ryan has become the de facto ideological and intellectual leader of the contemporary GOP. His agenda of turning Medicare into a voucher program, bloc-granting and taking the meat axe to Medicaid, drastically cutting spending on virtually every other government program (except defense, natch), and, yes, privatizing Social Security has been called many things, from courageous and bold (by countless conservatives) to “thinly veiled Social Darwinism” (by Obama) and “right-wing social engineering” (by Newt Gingrich). What you cannot call it is vague or vacuous or mealy-mouthed — all words that have been attached to the man at the top of the ticket.

So this was not a safe or conventional pick — not a pick motivated by winning a state (as Portman would have partly been regarding Ohio or Marco Rubio would have partly been regarding Florida). This was a pick about ideas, about policies, about core convictions. But it was also a pick driven by political weakness. All along, Team Romney’s bedrock strategy has been to make the 2012 election a clean referendum on Obama’s economic management and leadership, an election about unemployment, growth, and wages. In elevating Ryan, what Team Romney has done is execute a sharp U-turn, embracing the theory that 2012 will not be a pure referendum but a choice election, and one in which the two sides’ contrasting approaches to the deficit, debt, entitlements, and taxes will take center stage. And while this is surely not a Hail Mary pass on the order of John McCain’s selection of Sarah Palin, it is almost as much, as some Romneyites admit, an attempt to (pardon the expression) change the game.

All of which helps explain why the Obamans are grinning madly. It’s not simply that they, too, see the pick as an admission by Team Romney that its strategy was failing. Or that Ryan doesn’t clearly pass the test of being (and, crucially, looking) ready to be president. Or that his utter lack of private-sector bona fides undercuts, however mildly, Romney’s attacks on Obama for lacking same. It’s that Chicago and the White House perceive this as a broader capitulation regarding the core dynamic of the race: an acceptance of the “choice election” framing, which is exactly the frame that the incumbent and his people have embraced and attempted to propagate from the start.

And just why have they done that? Because they knew full well that if the race were purely a referendum on Obama, they would likely lose — but if bright lines could be drawn on values and visions regarding fiscal choices, that was the kind of election they could win. This was why Chicago was planning to hang the Ryan budget around Romney’s neck regardless of whether the congressman was on the ticket or not. Obama’s data jockeys have been polling and focus-grouping on this for months, and they are over the moon about what they have found. And while that data is guarded by lock, key, and Uzi-toting thugs (kidding — sorta), anyone interested in the topic should take a look at the work that Stan Greenberg and his team at Greenberg Quinlan Rosner did recently on the Ryan agenda and its electoral implications for Democracy Corps. To put it mildly, their conclusion is fairly bracing:

At the outset, the Ryan budget (described in Ryan’s actual language) barely garners majority support. And voters raise serious doubts when they hear about proposed cuts — particularly to Medicare, education, and children of the working poor. President Obama’s lead against Romney more than doubles when the election is framed as a choice between the two candidates’ positions on the Ryan budget — particularly its impact on the most vulnerable. The President makes significant gains among key groups, including independents and voters in the Rising American Electorate (the unmarried women, youth, and minority voters who drove Obama to victory in 2008).

The crucial question, to be sure, will be what the small sliver of undecided voters conclude when the dueling cases of each side are put to them. But however the chips fall and the cookies crumble in the coming Ryan-centric fracas on the hustings, at the conventions, and on the debate stages this fall — side note: Biden versus Ryan, holy moly, get your ringside tickets now! — it’s hard not to argue that Mitt Romney has done the country a major favor. No more hide-and-seek. No more guessing games. No more theorizing about what President Willard would do if he found himself behind the biggest desk of all. With Romney and Ryan now joined at the hip, the choice and the stakes of 2012 are as clear as day. As a man with no knack for memorable phrases once memorably said: Bring ‘em on.