For one of the clearest illustrations yet of the complex and unpredictable nature of the Syria strike voting dynamics in Congress, consider the Arkansas delegation and its pair of statewide candidates.

When he was first a candidate for the Senate, Democrat Mark Pryor backed a Republican president, George W. Bush, when he sought congressional authority to attack Iraq to prevent its threatened use of chemical weapons. But this past weekend, Pryor announced that he’ll almost certainly vote against a resolution backing the president of his own party, who wants to launch military strikes against Syria for using chemical weapons.

Barack Obama, he said, has not proved “a compelling national security interest,” defined “a mission that has a definitive end-state” or built an international coalition to collaborate in an attack.

Pryor’s 2014 challenger, Rep. Tom Cotton, last week completed his own even faster whiplash-inducing maneuver — going the other way.

Cotton won the House seat covering the fertile expanses south and west of Little Rock last year by campaigning against whatever policies Obama advocated, at home or abroad. But, even before Obama asked Congress for backing on Syria, the freshman congressman had emerged as one of the most vocal and enthusiastic proponents in either party of the president’s approach.

American action is needed, he said, to uphold international opposition to chemical weapon use, reassure Israel and other Middle East allies and preserve the global credibility of a president he generally disdains. “Put simply, our core national security interests are at stake,” he said in direct rebuttal of the Pryor view.

These opposite-spinning evolutions are a reminder that, whenever the “all politics is local” aphorism doesn’t explain how electoral rivals ended up in the same place, the “all politics is situational” corollary probably helps explain why they’re not.

In the fall of 2002, 3 in 5 Americans favored going to war to end Saddam Hussein’s dictatorship. So there was minimal downside to Pryor agreeing with the GOP incumbent, Tim Hutchinson, on Iraq and engineering his solid victory by emphasizing their ample differences elsewhere.

Now, 3 in 5 Americans oppose using American military might to punish Bashar al-Assad, with the ratio much more lopsided in unscientific online polling in Arkansas. And Pryor is the most endangered incumbent senator in the nation, the only Democrat in his delegation seeking a third term in a state that gave Obama just 37 percent of the vote last fall.

So he has every reason to vocally oppose the use of military force, because splitting with Obama to do what’s popular back home will surely reinforce his “Arkansas comes first” campaign mantra.

Cotton’s motivations are only a little more difficult to understand.

His high-profile Syria hawkishness underscores his military résumé (Army tours in Baghdad in 2006 and Afghanistan in 2008) and his developing expertise in world affairs, two calling cards he hopes counter arguments that he won’t’ be ready for the Senate at age 37, after a single House term. He will argue that reasoned independence from the party mainstream (the state’s three other GOP House members and GOP senator, John Boozman, are all reliable “no” votes) is just what the Senate needs right now. And he can gamble that by next fall, his race will be more about domestic issues — such as the economy and health care — no matter what happens in the Middle East.

On the other hand, Cotton has reason to worry that his internationalism will annoy the often-isolationist conservative activists he’s counting on as his financial and electoral base.

The Pryor and Cotton positioning is fascinating for another reason: So far, there’s no other race where members of Congress opposing one another for the same Senate seat have staked out opposing positions on Syria.

Louisiana is the only other state where the 2014 Senate contest looks certain to put an incumbent against a challenger from the House. Neither Democratic Sen. Mary L. Landrieu nor Republican Rep. Bill Cassidy has said anything to suggest how they’ll fall off the fence, which puts them in the company of most members of their delegations. Like Pryor, Landrieu is seeking re-election in a state where Obama got trounced last time, but her voting record this year has suggested she’s running much less scared than he is.

In Hawaii, Democrats won’t be able to look for a Syria split to help them decide in next year’s primary between appointed incumbent Brian Schatz and his main challenger, Rep. Colleen Hanabusa; both liberals are unambiguously against an intervention.

The same looks to be just as true of the three House conservatives seeking the GOP nomination for Georgia’s open Senate seat: Paul Broun and Phil Gingrey are locked-in “no” votes, and Jack Kingston seems very inclined to join them.

Six elections ago, four incumbent Senate Democrats were challenged for re-election by Republican members of the House. Three of them won that November, but the votes they had cast a month before on the Iraq War were in no way dispositive; all eight lawmakers voted “yes.”

That’s a precedent that makes the current cocktail of odd alliances, muddled partisanship, nuanced ideology and political maneuvering all the more fascinating.