"That sound you hear? It's the fat lady singing," says Chris Cillizza at The Washington Post. With a clean sweep of three primary contests on Tuesday, Mitt Romney all but sealed the Republican presidential nomination. His closest rival, Rick Santorum, is still making a last stand in his home state of Pennsylvania, which holds it primary on April 24, but the political world seems to have moved on. Romney himself is dropping plenty of not-so-subtle hints that he's focused on President Obama — and Obama seems more than willing to get the contest started. Here, six signs that the general election is underway:

1. Romney is done talking about his GOP rivals...
At his victory speech in Wisconsin on Tuesday night, Romney didn't mention any of his primary rivals by name, not "even to congratulate them on a good race," says Cameron Joseph at The Hill. It's a "notable deviation from his previous election-night speeches." This forces the GOP wannabes "to the sidelines" and puts them "firmly in his rear-view mirror at last," says Jonathan Martin at Politico.

2. ...And is focusing on Obama instead
Instead of name-checking Santorum and Co., Romney hammered the president's handling of the economy — potentially Obama's greatest weakness. He also said Obama was trying to "transform" the country into a "government-centered society," whereas he would "restore" the free-market values that made America the "powerhouse of the world." Expect to hear those lines more than once, says Frank James at NPR, as Romney tries to frame the race "as a referendum on the sitting president" who "can be blamed for trouble in the economy."

3. Obama is singling out Romney by name...
This week, the president "referred to Romney by name for the first time in a speech," says Tom Cohen at CNN. Obama blasted Romney for supporting a House GOP budget that calls for sharp spending cuts for the poor and the elderly, slamming it as a "Trojan horse" that would introduce "social Darwinism" to America. Obama wants to make sure that "Romney owns" that unpopular budget, says MSNBC's First Read

4. ...And bashing the GOP
Obama's attack on the budget was a full-throated assault on trickle-down economics and other sacred tenets in Republican ideology, underscoring a "clear choice" between the two parties, says Kenneth Walsh at U.S. News & World Report. Instead of reaching a hand across the aisle, Obama went out of his way to paint the modern-day GOP as extreme, saying even Ronald Reagan "could not get through a Republican primary today." 

5. Obama and Romney are speaking at the same events...
Obama delivered his assault on the GOP at the Newspaper Association of America conference in Washington, D.C. Romney took the same podium a day later, and accused Obama of running a "hide-and-seek" campaign that disguises his real policy goals. 

6. ...And they're launching attack ads 
Obama's re-election campaign is launching new "ads in swing states linking Romney to 'Big Oil,'" says Cillizza. The Romney campaign has responded with a short web video accusing Obama of "slinging mud" to "cover up his failed energy policies." Indeed, "the rhetoric has reached October-like levels," says Martin. Romney and Obama are each trying to frame the other as "out of touch," with Romney claiming that Obama spends his days "flying on Air Force One, surrounded by an adoring staff of true believers." Obama, for his part, has mocked Romney for praising the Republican budget as "marvelous," in an attempt to "reinforce the idea that Romney is a very wealthy man lacking the common touch," says James.

Sources: CNNThe Hill (2), MSNBCNPRPolitico (2), U.S. News & World ReportWashington Post