Once again, Republicans seem downright obsessed with Barack Obama.

Sen. Marco Rubio (R-Fla.) has spent plenty of campaign time, and no small amount of airtime in the debates, attacking the president and his track record. Rubio's messaging has focused on positioning Obama as an extremist who wants to "fundamentally transform" America from its traditional values toward a progressive agenda. Other candidates have attacked Obama for incompetence, but Rubio insists that's a mistake.

In fact, he repeatedly insists that it's a mistake. During Saturday night's debate, Rubio twice said, "Let's dispel with this fiction that Barack Obama doesn't know what he's doing. He knows exactly what he's doing." Rubio started a third repetition of the line but got interrupted by New Jersey Gov. Chris Christie, who ripped it as "a memorized 25-second speech." Undaunted, Rubio got the message line in once more during the debate, and later pledged to keep using it.

"That's what I believe passionately," Rubio later told ABC's George Stephanopoulos. "It's one of the reasons why I'm not running for re-election to the Senate and I'm running for president. This notion and this idea that somehow all this is an accident — ObamaCare was not an accident, Dodd-Frank was not an accident, the deal with Iran was not an accident."

Most observers felt Rubio came off poorly in the exchange with Christie, but others found Rubio's messaging solid. No less a conservative authority than Rush Limbaugh defended Rubio on Monday. "The governors will not admit who Obama is," Limbaugh declared. "To people inside the Beltway, to the elites, to the establishment, Obama's just the latest Democrat to come along. … They don't see what Obama's doing as anything except maybe a young, inexperienced — this is Christie's point — incompetent boob. Well, that's not who Obama is."

Limbaugh frames the who-is-Obama debate perfectly — at least for the Republican primaries. If Obama is a well-meaning incompetent as Christie appears to argue, then the solution for the post-Obama era is more competence: governors. If the danger from Obama is effective extremism, then the antidote isn't establishment incrementalism but an equal and opposite conservative activism driven by relative outsiders. Rubio has himself in mind, but that same argument could apply to Ted Cruz, also a one-term senator, or to Ben Carson. It might have applied to Donald Trump, but the billionaire real-estate tycoon has sold himself as a pragmatist who also sees Obama as a case of incompetence, as Limbaugh noted on air Monday.

This argument cuts to the heart of the Republican primary fight between the candidates. They had better settle that argument quickly, however, because for the general electorate, the effort to define Obama has long been over. The voters who will decide the general election want to define their future, and to get a fresh start. They don't want to rehash the same old political battles that have dominated the past eight years.

In conducting research for my upcoming book Going Red (April 12, Crown Forum), I traveled to seven key swing counties in states Republicans must win to recapture the White House. I spoke with more than 100 voters, activists, and elected officials at the local, state, and federal levels, and to Republican officials about what went wrong in 2008 and 2012 for the GOP. The results of the 2008 election have much to do with organization, timing, and economic issues on which the Republican Party had limited control, but still offer important lessons.

In 2012, however, Republicans had more opportunities for victory. Much of the failure to grasp that victory was again due to organizational failures and a lack of engagement. One key lesson, however, has to do with the manner in which Mitt Romney framed his argument in regard to Obama. Rather than focus on a positive message that looked to a Romney-led future, the campaign became focused on Obama as both incompetent and extreme.

This created a dissonant reaction among voters who supported Obama in 2008 as a historic figure, but might have been persuaded to change directions in 2012 had Republicans focused primarily on something other than a litany of Obama's failures. One Florida voter in a younger, gentrifying area of Tampa told me of a neighbor that put an Obama sticker on his refrigerator in the first election, but like some in the area, had begun to be disillusioned by Obama after four years. However, they retained that emotional connection to their 2008 vote, seeing it as a protest against politics as usual and a hope for a better public-policy environment. Constant Republicans attacks on Obama not only felt like personal attacks on their own judgment, but also the very kind of politics they believed they rejected in 2008.

At least in that cycle, Republicans had a legitimate reason for basing their campaign on the failures and/or excesses of Obama's presidency. He was, after all, an incumbent seeking re-election. But in 2016, Obama's presidency will belong to the past, not to the future. Republicans have an opportunity to reset their approach and engage with voters in key demographics much more successfully. If they spend their time attacking Obama rather than focusing on their own positive vision for America, however, those voters will once again get turned off by the same politics they have experienced over the past eight years, and the GOP will miss a great opportunity to expand its reach and its message.