For nearly a full year now, President Obama's job-approval rating has been stuck below 50 percent in the Gallup Poll. That means a plurality-to-a-majority of Americans expressed disapproval of the job he is doing for the past 11 months.

The last time Obama hit 50-percent approval was 11 months ago — late June 2013. Since then, thanks to a number of problems such as the still-anemic economy and the bumpy rollout of ObamaCare, coupled with a series of crises with the IRS, Benghazi and now the Departments of Veterans Affairs health care system, it has been mostly downhill. For the week ending May 18, Obama averaged 44 percent approval, 51 percent disapproval.

Should Democrats running in this year's congressional elections be worried about the president's persistent low ratings? In a word, yes. History suggests that presidents with job approval ratings below 50 percent at this point cost their party seats in the midterm elections. Take a look:

  • The last time a president was below 50 percent approval going into a midterm election was 2006, and that president was George W. Bush. In late May 2006, Bush, embroiled in an Iraq War gone bad, had a Gallup job approval of 36 percent. In the congressional elections six months later, Republicans lost 30 seats and control of the House of Representatives for the first time in 12 years. They also lost six Senate seats, giving Democrats a 51-49 majority.
  • Before that, it was Bill ClintonWilliam (Bill) Jefferson ClintonCourt questions greens’ challenge to EPA chemical rule delay The only way out of this mess Federal court tosses out Obama-era rule requiring financial advisers to act in customers' best interests MORE in 1994. In early June of that year, Democrat Clinton was at 46 percent approval. In the November elections, Democrats lost 54 House and eight Senate seats, giving Republicans control of both houses of Congress for the first time in 40 years.
  • In 1978, Democrat Jimmy Carter was at 44 percent approval in early June. His fellow Democrats lost 15 seats in the House and three in the Senate. But thanks to huge post-Watergate majorities going in, neither of the losses were enough to cost Democrats control of either house.
  • That brings us to 1974, a disastrous midterm year for the party of a scandal-ridden president. In early June 1974, Republican Richard Nixon was mired in Watergate. His Gallup job approval was a paltry 28 percent. Two months later, he resigned, turning over the White House to Gerald Ford. Ford took office amid a wave of public relief. But Nixon's departure was not enough to hold back the Watergate flood. Republicans lost 48 House seats and four more in the Senate, giving Democrats overwhelming majorities in both houses of Congress and making political life difficult for Ford in his final two years in office.
  • Going back to 1966, Democrat Lyndon Johnson, overwhelmed by Vietnam, had a 48 percent approval rating in early June. In the fall elections, Democrats lost 47 House seats and three in the Senate.  But although losses were considerable, they were not enough to cost Democrats their majorities thanks to the Johnson landslide of 1964.

Nonetheless, Johnson chose not to seek reelection two years later.

Make no mistake: This history is not lost on Obama and his political strategists. They know they have trouble snarling at their heels and they are pedaling as hard as they can to outrun it. Republicans need to win six Democratic seats to take over the Senate and seem safe in holding onto their majority in the House. That's why the president is out on the fundraising trail every chance he gets. His pleas at a flurry of Democratic dinners and galas in Texas, New York City, Chicago and Washington in recent days and weeks broadcast his worry:

"We've got to win these midterms," Obama said last week at a Democratic Congressional Campaign Committee fundraiser in Potomac, Md. "And we've got to be serious about it. We have to have the same sense of urgency that we do when presidential candidates are at the top of the ballot. We turn out during presidential elections; we don't in midterms. Our voters do not. And that's why an event like this is so important. We know how to turn folks out. We've got to make sure that we've got the resources to do it."

Obama is pitching hard against history. Republican control of the House and Senate during his last two years in office is his worst nightmare. If he feels hamstrung trying to do the things he wants to do with Republicans ruling one house of Congress, GOP majorities in the House and Senate will fit like a straitjacket. And his legacy will be largely out of his control.

Benedetto is a retired USA Today White House correspondent and columnist. He now teaches politics and journalism at American University and The Fund for American Studies program at George Mason University.