Mitt Romney’s choice of Paul Ryan as his nominee for vice president achieved something remarkable in the modern history of U.S. presidential elections. He made both sides ecstatic.

Conservatives are in a state of euphoria

Ryan, despite his many deficit-expanding votes during the Bush administration, is a true believer’s true believer. Every doubt that conservatives have about Romney is matched by the faith that they place in Ryan. Romney, amazingly, just made himself the dullard figurehead of his own administration.

But liberals likewise profess themselves enthused.

Medicare is back on the menu, boys! Now there’s just no way Romney will be able to run away and hide from the draconian, social welfare-slashing Ryan budget. A million senior-scaring attack ads are likely already in production; Florida has a brand-new boogeyman. Some pundits are boldly calling the choice a Hail Mary act of desperation; only someone watching the election slip away would hand such a golden opportunity to his opponents.

But before liberals start cheering too hard, they might want to think this through. If the Romney-Ryan team wins, a future in which Paul Ryan eventually becomes president of the United States becomes more likely than not. That’s a future in which the New Deal is repealed. So be careful what you wish for. No doubt there are many Democrats rubbing their hands in glee in contemplation of reviving some version of the ad that featured an actor playing Paul Ryan pushing a grandmother in a wheelchair off a cliff. But the smarter ones are worried.

If Paul Ryan is an extremist and his proposals are so unpopular, how has he won election seven times in a Democratic district?

His lowest share of the vote was 57 percent — in his first race. He routinely wins over two-thirds of the vote. When Obama swept the nation in 2008, he carried Ryan’s district by four points. But at the same time, Ryan won reelection with 65 percent of the vote, meaning that a fifth of Obama voters also voted for him.

Paul Ryan has pointed out to me that no Republican has carried his district for president since Ronald Reagan in 1984. “I have held hundreds of town-hall meetings in my district explaining why we have to take bold reform steps, and I’ve found treating people like adults works,” he told me. “All those ads pushing elderly woman off the cliffs don’t work anymore if you lay out the problem.”

Democrats know that Paul Ryan has Reaganesque qualities that make him appealing to independent, middle-class voters.

Take the cover story on Ryan that the Isthmus, a radically left-wing Madison, Wis. newspaper, ran on him in 2009. “Ryan, with his sunny disposition and choirboy looks, projects compassion and forcefully proclaims dedication to his district,” the story reported. “And he’s proved he is not unyieldingly pro-corporate, as when he recently joined in condemnation of AIG ‘retention’ bonuses.”

Paul Ryan’s ideas aren’t that novel or scary.

The idea of “premium support” for Medicare, which would change the program’s one-size-fits-all policy to a private-insurance model with public options, was endorsed by a bipartisan commission appointed by Bill Clinton back in the 1990s. Late last year, Ryan announced a new version of his proposal with a new partner signing on: Democratic senator Ron Wyden of Oregon, who first achieved political prominence as an advocate for seniors.

Paul Ryan puts Wisconsin and its ten electoral votes in play.

Polls have shown that President Obama holds a five to seven point lead in Wisconsin — significant, but much less than Obama’s 14-point margin in 2008. With Ryan on the ticket, polls show the race is dead even.

If Republicans were looking for a superior candidate, they’ve found it in Paul Ryan.

His maiden speech as the GOP vice-presidential candidate was perfectly pitched:

We won’t duck the tough issues . . . we will lead!
We won’t blame others…we will take responsibility!
We won’t replace our founding principles . . . we will reapply them!

Echoes of Ronald Reagan at his best.

Ryan will bring in a flood of donations from overjoyed conservatives and tea-party members.

Romney had a problem with energizing the GOP base. That problem is now solved, and that will make it easier to pump up conservative turnout.