Five things we learned Tuesday

(CNN) -- Republican presidential frontrunner Mitt Romney had a big night Tuesday, sweeping primaries in the District of Columbia,
Maryland and Wisconsin and putting more distance between himself and closest pursuer Rick Santorum in the race for delegates.

Here are five things we learned from Tuesday's vote:

Santorum's coalition fell apart

Wisconsin Republicans didn't just side with Mitt Romney on Tuesday -- they rejected Rick Santorum.

Pawlenty: Santorum 'lashing out'

Santorum: 'Pennsylvania, you know me'

Santorum looking ahead to PA primary

Obama looking ahead to Romney face-off?

Make no mistake: Santorum campaigned hard in Wisconsin, raising the stakes for the primary.

He ignored Maryland, the night's other big prize, and hit the Wisconsin bowling alley-and-cheese curd circuit, telling voters how a win there would shake up the GOP race.

"Wisconsin will send a sound around this country, like the sound of Lexington and Concord," Santorum said at a rally in Beaver Dam. "You will be the shot heard 'round the world."

That shot was never fired, because the Santorum coalition actually voted for Romney.

Big sweep for Romney

Evangelicals, tea party supporters, those supporting "traditional values" and people calling themselves "very conservative" went Romney's way, exit polls showed.

And one of Santorum's key messages -- that Romney can't stand up to Barack Obama because of his support for a health insurance mandate in Massachusetts -- also fell flat.

On the exit poll question of "Who do you trust to handle health care?" it was Romney who came out on top.

But Santorum will fight on

Over the last 10 days, the media and the Republican establishment seemed to come to a consensus -- cheered on by the Romney campaign -- that a Santorum loss in Wisconsin would spell doom for his campaign.

That may be true given Romney's wide delegate lead and his snowballing momentum, but Santorum showed no signs of quitting Tuesday, promising to forge ahead through May, when a slew of conservative Southern states will cast votes.

Santorum: "It's halftime"

He delivered his concession speech in the tiny town of Mars, Pennsylvania, boasting of his intimate connection with the state he represented in Congress for 16 years.

In an interview on CNN, Santorum's chief strategist John Brabender claimed that wins in Pennsylvania on April 24 and Texas on May 29 would propel his boss to the nomination over Romney -- a dubious claim considering that victories in both states would do little to cut into Romney's delegate advantage.

But even if a Pennsylvania win would somehow help secure the nomination for Santorum, the opposite is also true: A loss in his home state would cripple his campaign.

It's possible that might happen, and the Romney campaign knows it, which is precisely why the frontrunner will ride his latest burst of momentum into Pennsylvania on Wednesday for two days of campaigning on Santorum's turf.

Big-name endorsements finally had an impact

We've written in this space before that endorsements have been the fool's gold of this election cycle: attention-grabbing and sought after, but ultimately not worth very much.

This was not true in Wisconsin, Tuesday's marquee battleground.

Romney was practically swimming in big-name endorsements in the run-up to the vote, thanks to a GOP establishment increasingly eager to end the Republican-on-Republican mayhem and pivot to the fall election against President Barack Obama.

Top conservatives like Marco Rubio, Mike Lee and Wisconsin's own Paul Ryan jumped on the Romney train last week, as did former President George H.W. Bush.

And leading Republicans as ideologically distant as Mitch McConnell and Jim DeMint expressed their desire to see the Republican primary fight wrap up, implicitly siding with Romney.

Wisconsin was paying attention.

More than 60% of Republicans said the Romney endorsements were a factor in their votes, and 33% called them an "important" factor. Most of those voters, of course, broke heavily toward Romney.

The message these new surrogates were pushing -- that Romney is the likely nominee even if he doesn't have the delegates yet -- appeared to resonate.

A huge majority of Wisconsin Republicans, 83%, said Romney is "most likely" to win the GOP nomination.

Embattled governor has a posse

Exit polling out of Wisconsin revealed some bad news for Democrats and their organized labor allies: Republicans adore Scott Walker, their embattled governor who faces a recall election in June.

Walker's job is on the line thanks to his controversial push last year to roll back collective bargaining rights for state workers.

But the Republican base has his back.

According to exit polls, 82% of those who voted in Tuesday's primary approve of Walker as governor, and 71% "strongly" approve.

That emphatic support will be crucial for Walker as he faces off against his probable Democratic opponent, former Milwaukee mayor Tom Barrett, in a race likely to be decided by a tiny slice of undecided voters.

A poll from NBC News and Marist released last week showed that Wisconsin registered voters are evenly divided on Walker, with 48% percent approving of his job performance and 48% disapproving.

Only 6% of Wisconsinites in the poll said they were undecided about which candidate to get behind.

The formula for Walker, then, is pretty straightforward: sway most of the undecided voters, and get those who "strongly" approve of his record to the polls on June 5.

Barack Obama will be the Democratic nominee

OK, we already knew that.

But according to CNN's delegate estimate, the president collected enough delegates in Maryland and the District of Columbia on Tuesday night to formally secure the Democratic nomination.

Now we know for certain that Obama will accept his party's nomination at the Democratic National Convention in Charlotte.

The news officially puts to rest the silly chatter about a Democratic primary challenger (Howard Dean! Russ Feingold!) that bubbled up in 2010 during the most dismal moments of Obama's presidency.