Editors' pick: Originally published Jan. 19.

Politics is often about knowing when to make enemies and when to make friends.

Eight years ago, Hillary Clinton lost a bitter battle with Barack Obama for the Democratic presidential nomination. But on Sunday in an NBC-hosted debate from Charleston, S.C., the former New York senator made clear that she wants to be closely associated with his presidency.

In comments on the economy, Wall Street regulation, healthcare and negotiating with Iran, Clinton heaped plaudits on the man that she and her husband Bill once derided as inexperienced and naive. This time around, with the Iowa Caucuses just three weeks away, Hillary's appreciation or even affection for the president was effusive, or as Politico'sGlenn Thrushput it "Clinton hugged Obama so hard he needs new ribs."

There's a strategy at work here, and it's quite simple.

Obama's most recent job approval rating stands at 47%, according to a Gallup Poll conducted Jan. 4-10. That figure is well within the margin of error of the 50% threshold needed to all but assure election of the party's nominee, explained Doug Sosnik, a Democratic strategist in a piece for Politico in July.

Put aside for the moment that Sosnik used to work with Bill Clinton and certainly has a horse in the current race. Focus instead on that 47% number -- it doesn't sound like much but it could put Clinton into the White House come November.

In eight of the last nine presidential elections, the candidate of the incumbent party was victorious whenever the standing president's job approval rating was near or above 50% prior to the start of the general election.

The only exception to Sosnik's theory was George W. Bush's 2000 victory in which he lost the popular vote and was declared the winner by the Supreme Court following a tumultuous legal process. In all the other cases, if the incumbent president's rating was near or above that 50% line, that party's nominee strode to victory. If it was less than 40%, that party's candidate was defeated.

"The job approval ratings of the incumbent president, regardless of whether they are running for re-election, serve as a proxy for the electorate's mood and have historically been the most accurate predictor of election outcomes," he wrote.

Going back to 1980, there were five elections in which the incumbent party's leader's job approval rating was over 50% prior to the general election, and three times when fell under 40%.

In the plus column: Ronald Reagan's re-election in 1984; George H.W. Bush's election in 1988; Clinton's re-election in 1996; Bush II's re-election in 2004; and Obama's re-election in 2012. In the negative column: Reagan's 1980 victory over incumbent Jimmy Carter; Bill Clinton's victory over Bush I in 1992; and Barack Obama first-term victory when George W. Bush left office with a job favorability rating of a mere 33%.

The underlying reason probably has to do with the domestic economy. Yes, the global economy could tank, and terrorism could flare up, but the U.S. economy remains steady, having added 292,000 new jobs in December as unemployment remains at 5%, its lowest since 2008, according to the Labor Department. Meanwhile, Obama's job approval rating has held close to that 50% marker, far from the low of 38% he hit in September 2014.

"Obama's relative popularity continues to pose a challenge for Republicans intent on taking back the White House," Sosnik said. "Unlike his predecessors whose popularity varied greatly throughout their time in office, Obama's all-important job approval ratings have remained quite durable."

And for Hillary Clinton, who still seems to have the inside track to the Democratic nomination, that's all she needs to know to stay friends.