With Rep. Paul Ryan officially in the mix as Mitt Romney's vice presidential pick, the 2012 race for the White House was fully engaged Monday, as all four members of the two major-party presidential tickets campaigned in swing states.

Both President Obama and Ryan were in Iowa, while Romney, the all-but-official Republican nominee, campaigned in Florida. Meanwhile, Vice President Biden was in North Carolina, hitting a state the Republican ticket visited over the weekend.

Obama began a three-day bus tour through Iowa with a stop in Council Bluffs. The president used the opportunity to immediately go after Ryan on an issue with special resonance in a major agricultural state: the failure of the Republicans, who control the House, to bring a Senate-passed farm bill to a floor vote. That legislation contained a relief measure to help drought-afflicted farmers like those in the Midwest.

Ryan, an intellectual leader of the House Republicans and Budget Committee chairman, was an inviting target for Obama.

OBAMA: "Unfortunately right now, too many members of Congress are blocking the farm bill from becoming law. (Crowd boos.)"I am told that Gov. Romney's new running mate, Paul Ryan, might be around Iowa the next few days. He is — (boos) — one of the leaders of Congress standing in the way.
"So if you happen to see Congressman Ryan, tell him how important this farm bill is to Iowa and our rural communities. (Applause.) We've got to put politics aside when it comes to doing the right thing for rural America and for Iowa." (Cheers, applause.)

House Republicans decided against bringing the bill to the floor in part because of divisions in their ranks. Agricultural subsidies in the bill are opposed by some Republican legislators, who view them as corporate welfare at odds with their free-market principles.

Appearing at the Iowa State Fair in Des Moines, Ryan had his own question for Iowans to ask Obama:

REP. RYAN: "My guess is the reason President Obama isn't making it here from Council Bluffs — because he only knows left turns. (Crowd cheers, applause.)"You know — but as you see the president come through on his bus tour, you might ask him the same question that I'm getting asked from people all around America, and that is where are the jobs, Mr. President?" (Cheers, applause.)

Ryan stopped to deliver brief remarks at The Des Moines Register's soapbox, a stage used by visiting politicians during election season to deliver their messages to Iowans.

It was at the same location last year that Romney uttered the famous line "Corporations are people, my friend," in response to hecklers.

Ryan was heckled, too. But he didn't deliver a response that appeared, at first blush, to be gold for the opposition, as Romney did last summer.

RYAN: "We're used to this in Wisconsin — oh yeah."

Ryan alluded to the superheated political climate in the Badger State since Republican Gov. Scott Walker and his allies in the state legislature decided to take on the public employee unions.

Romney's selection of Ryan, a favorite with the conservative base, has made it easier for the president to make an argument he's tried all along: that the general election is a choice between two starkly different visions of the nation's future.

Obama used one of his favorite words, "choice," at least eight times:

OBAMA: "I'm going to spend the next three days driving all across this state, just like I did in 2007, from — from Council Bluffs to the Quad Cities, because once more you face a choice in November. And that choice could not be bigger."It is not just a choice between two candidates or two political parties. More than any other election in recent memory, this is a choice between two fundamentally different visions of this country and the path that we have to take. And the direction that you choose when you walk into that voting booth in November is going to have an impact not just on your lives but on your children's lives, your grandchildren's lives for decades to come. (Cheers, applause.) This one counts."

Romney's campaign had previously been largely based on the notion that the election amounted to a referendum on the president's performance.

Based on the language both he and Ryan used at campaign appearances over the weekend and again on Monday, the Republicans seemed to have decided to accept Obama's premise that the election is a choice — but to hang onto the earlier strategy that it is a referendum, too, in something of a one-two punch.

For instance, Ryan said Monday at the Iowa State Fair:

"And so what you will see from us is this: We owe you a choice. You are our fellow citizens, and what we want to do is give you the choice so you can decide what kind of country you want to have. What kind of people do you want us to be?"

Meanwhile, campaigning in St. Augustine, Fla., Romney told an audience the president deserved failing grades and only one term for his performance.

"He said that he would be able to measure progress and measure success by a whole series of his own standards. Number one was being able to create jobs. But I hope he understands that he hasn't done that: 23 million Americans out of work or stopped looking for work and can't find the jobs they need to put food on the table for their families."It's unacceptable. It's a moral failure for a nation as successful as ours not to have created these jobs. Mr. President, by your own measure, you failed to deliver the jobs Americans need. (Cheers, applause.)"

Campaigning in Florida, long a warm-weather haven for retirees, Romney renewed a charge — by now repeatedly discredited by journalistic fact-checkers — that Obama cut hundreds of billions of dollars from the Medicare program as part of the Affordable Care Act.

ROMNEY: "The president's idea, for instance, for Medicare was to cut it by $700 billion. That's not the right answer. We want to make sure that we preserve and protect Medicare."

(Republicans initially charged Obama with cutting $500 billion from Medicare. NPR's Julie Rovner explained in a Q&A earlier this year that hospitals and other health care providers volunteered to take the cuts in payments with the expectation they would come out whole since more patients would be insured.)

Biden, for his part, was in Durham, N.C., where he also zeroed in on the differences between the tickets.

An excerpt from Politico of Biden's appearance at a rally:

"Now that Gov. Romney has selected his running mate, those ... differences are even more stark," Biden told 900 people here. "The reason I say that, Congressman Ryan has given definition to the vague commitments that Romney's been making.""... And ladies and gentlemen, we know, we know for certain, what I've been saying for a long time, there is no distinction, let's get this straight, there is no distinction between what the Republican Congress has been proposing the last two years, actually the last four years, and what Gov. Romney wants to do."Copyright 2016 NPR. To see more, visit http://www.npr.org/.