Well, the Adrian Peterson era didn't last long in New Orleans. After four games and 81 rushing yards, the Saints have shipped off the free-agent signing to the Cardinals in exchange for a 2018 conditional sixth-round pick. It's not hard to understand why both teams would be on board to make the deal.

The Saints might have known it was time to move on from the 32-year-old Peterson in Week 1, when he harangued coach Sean Payton on the sideline for not running the ball frequently enough in the middle of a 29-19 loss to the Vikings on Monday Night Football. Peterson's role in the offense, despite Payton's preseason claims to the contrary, has been murky at best. He has felt like a useless appendage in a Saints backfield that has been built around Mark Ingram and rookie Alvin Kamara.

With Payton wanting to focus the backfield around two backs each week, Peterson played just six snaps against the Dolphins in London in his final game with the Saints before New Orleans' bye. Given that Peterson can't replicate Kamara's skills, Peterson was likely going to be a third-string back the rest of the way, barring an injury to Ingram. If Peterson played special teams, the Saints might have justified keeping him around, but New Orleans was likely trying to save both the $705,882 they owe Peterson for the remainder of the year, and a headache.

The Cardinals obviously have a need for a primary running back after David Johnson dislocated his wrist in the season opener. The trade for Peterson might suggest that Arizona isn't optimistic about Johnson's chances of returning this season, despite the fact that Johnson is eligible to return from injured reserve in mid-November. Coach Bruce Arians has suggested the Cardinals are hoping to get Johnson back in the lineup by Christmas, which would be good for only the final two games of the season. If the Cardinals are out of the playoff picture or if Johnson isn't 100 percent, it would hardly be surprising to see Arizona keep Johnson sidelined for the rest of the season.

You might argue that the 2-3 Cardinals are already out of the playoff picture, given that their two wins have been over the lowly Colts and 49ers in games that went to overtime. The ascension of the Rams hasn't helped Arizona's chances, either. With Carson Palmer & Co. facing one of the league's toughest remaining schedules, ESPN's Football Power Index gives the Cardinals just a 6.9 percent chance of making it to the postseason, down from 44.3 percent before the regular season began.

The trade for Peterson suggests the Cardinals aren't giving up, which shouldn't be a surprise. This is a veteran team built to try to win during the final moments in the careers of arguably the three most important people in the organization. Larry Fitzgerald is a free agent after the season and reports have suggested 2017 will be his last year. Palmer turns 38 in December and will consider his future after this season. The 65-year-old Arians fought kidney cancer last year. The Cardinals are staring down a rebuild that might be only months away from beginning. They can't afford to treat this like a lost season.

Adrian Peterson had only 27 carries in four games for the Saints, averaging 3.0 yards per rush. Photo by Stephen Lew/Icon Sportswire

While the Cardinals shouldn't trade future first-round picks to try to target a veteran who might keep them afloat (as the Raiders once did to acquire Palmer), their running back situation was a mess. They had replaced Johnson with Kerwynn Williams and then Chris Johnson, the latter of whom had been released in training camp and has now been released again. Neither back had been effective, with the duo combining to average an unreal 2.3 yards per carry. With David Johnson out of the lineup during the past four weeks, the Cardinals had cost themselves 0.23 wins with their rushing attack, according to ESPN Stats & Information, topping only the Giants.

The Cardinals have used Andre Ellington as their third-down back, but Arians is famously loathe to give Ellington a larger role in the offense. Peterson's skill set -- or relative lack of ability as a receiver and blocker -- should theoretically make him a good fit alongside Ellington. Arizona should be able to use Peterson as a two-down back and get him involved early and often.

It also helps that Arians' offense is built around keeping his quarterback under center. Just 13 percent of Arizona's run plays have come out of the shotgun this season, the second-lowest rate in the league. Peterson hasn't run the ball much out of the shotgun in the course of his career, with just 135 of his 2,445 rushing attempts coming out of the shotgun or pistol, and he has been far better under center. AD has averaged 4.9 yards per carry under center and 3.7 yards out of the shotgun.

At the same time, though, the Saints were supposed to offer that benefit to Peterson too. They've run the ball out of shotgun only 19.4 percent of the time, which is 27th in the league, and 24 of Peterson's 27 carries this season came with Drew Brees lined up under center. Peterson has averaged 2.9 yards per attempt on those runs. The one saving grace in Peterson's defense might be that he has averaged a mere 0.9 yards before being hit by the first defender, which is 46th among 47 qualifying backs in 2017. Ingram is at 1.5 yards before contact per rush, which is also below average and suggests that a Saints team missing both of its tackles for most of the season hasn't been effective in creating holes for their power backs.

Adrian Peterson will likely see his workload increase after being traded to Arizona. Photo by Chuck Cook/USA TODAY Sports

The problem is that the Cardinals haven't been any better; their backs have gained just 1.5 yards before contact, which is 31st in the NFL and ahead of only the Dolphins. It's also plausible that Peterson has lost several steps and isn't fast enough to get to the hole. The former league MVP has more than 2,500 NFL carries if you include his playoff attempts. He's now two years removed from his last effective season, when he led the league in rushes, rushing yards and rushing touchdowns for the 2015 Vikings. Peterson didn't look good before or after suffering a knee injury last season, and he has been a subreplacement back this season. Throw in the 2014 season that he essentially missed via suspension and Peterson has had just one useful campaign in three-plus seasons.

I'd argue that logic is a little tortured. Peterson's missing 2014 season shouldn't hurt his chances of being effective in 2017; if anything, given that he basically spent a year on the sidelines without accruing carries or taking hits, it should have extended his career. I'm also not sure how much we should read into 37 carries from 2016 or 27 carries from this season on sample size alone; there are plenty of backs who have ugly three- or four-game stretches and manage to be effective after, which is really what Peterson's workload amounts to.

It's telling that the league expressed little interest in signing Peterson this offseason, and he had to wait until late April to come to terms with the Saints. The odds are certainly against him turning back the clock and looking like a franchise running back, even if Arians and Arizona have managed to turn around the career of fading veterans such as Chris Johnson and Dwight Freeney in years past. Peterson also won't solve Arizona's problems on defense, notably the gaping hole at cornerback across from Patrick Peterson that teams have been exploiting during the past season and a half.

Given that the deal is for a conditional sixth-round pick in 2018, though, it's hard to argue that the Cardinals are giving up much for a player who could shore up a major position of need. Paying a little more than $700,000 and giving up a late pick for a player whose upside might still be as a league-average starting running back isn't much at all. Peterson might be able to both improve the Arizona running game and spark a Cardinals play-action passing attack that ranks 29th in passer rating through five weeks. Desperate teams have taken far more desperate and damaging measures than the Cardinals did Tuesday.