For several years, debate over President Barack Obama's international policies has followed a simple partisan pattern.
Obama's top aides and most fellow Democrats, hailing the end of the Iraq war, supported his goal of lowering the U.S. profile abroad.
Most top Republicans, led by Obama's 2008 opponent Sen. John McCain of Arizona and his senatorial sidekick, Lindsey Graham of South Carolina, blasted withdrawal from Iraq as premature and charged that Obama's weak leadership has led to problems besetting Iraq and other Middle East trouble spots like Syria, Libya and Egypt.
But that pattern is beginning to break up amid indications the foreign policy debate in the 2016 elections may well become more complicated.
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Two political factors are primarily responsible:
Outspoken support for a reduced U.S. global role by one of the leading GOP presidential hopefuls, Sen. Rand Paul of Kentucky, and subsequent attacks on him from some potential 2016 GOP rivals, notably Texas Gov. Rick Perry.
Former Secretary of State Hillary Clinton's suggestion, in a lengthy interview with The Atlantic's Jeffrey Goldberg, that her criticism of Obama goes beyond the disclosure in her memoirs that she favored a bigger U.S. role in Syria, reopening their 2008 foreign policy differences on the eve of the 2016 Democratic campaign.
The GOP spat began when Paul, in an op-ed article in The Wall Street Journal, said he stood by his opposition to the 2003 invasion of Iraq. "We should not put any U.S. troops on the ground in Iraq, unless it is to secure or evacuate U.S. personnel and diplomatic facilities," Paul wrote.
Perry, responding in an op-ed in The Washington Post, called it "disheartening" to hear Republicans like Paul "suggest that our nation should ignore what's happening in Iraq."
And former Vice President Dick Cheney, an architect of U.S. policy in Iraq, alluding to Paul's positions at a forum sponsored by Politico, said, "Anybody who went through 9/11 who thinks we can retreat behind our oceans and we'll be safe and secure is -- I'm sorry, but they're out to lunch."
More recently, Paul became embroiled in controversy during an Iowa visit over a reporter's suggestion that he voted to cut aid to Israel. "Don't mischaracterize my position on Israel," he replied. In a 2011 balanced budget plan, Paul urged cuts in foreign aid but did not specify Israel.
The re-emergence of Iraq as a major foreign policy issue ensures that differences between Paul and his potential rivals will influence the GOP race. And if Clinton seeks the Democratic nomination, she has made it likely that Democrats could face a similar division.
In the Atlantic interview, she not only took a more muscular tone than Obama but suggested that his refusal to help President Bashar al-Assad's more moderate foes helped the more extreme Islamic State faction that now occupies much of Syria and Iraq.
"Failure to help build up a credible fighting force of the people who were the originators of the protests against Assad -- there were Islamists, there were secularists, there was everything in the middle -- the failure to do that left a big vacuum, which the jihadists have now filled," she said.
And when asked if she agreed with Obama's recent characterization of his foreign policy as "don't do stupid (expletive)," she said, "That's a good lesson, but it's more complicated than that. ... Great nations need organizing principles, and 'don't do stupid stuff' is not an organizing principle."
Criticism from one antiwar group and longtime Obama adviser David Axelrod illustrated the potential battle.
" 'Don't do stupid stuff' means stuff like occupying Iraq in the first place, which was a tragically bad decision," Axelrod said on Twitter. Clinton, of course, voted in 2002 to authorize the Iraq attack.
"Secretary Clinton, and any other person thinking about seeking the Democratic nomination in 2016, should think long and hard before embracing the same policies advocated by right-wing war hawks that got America into Iraq in the first place and helped set the stage for Iraq's troubles today," said Ilya Sheyman, executive director of MoveOn Political Action.
While that misrepresents Clinton's statements, it signaled the degree to which her views may well prompt primary opposition from her left.
Potentially, this could prevent an odd situation in which a Republican nominee Paul was closer to Obama's position than a Democratic nominee Clinton.
Carl P. Leubsdorf, is the former Washington bureau chief of the Dallas Morning News.