On the eve of the midterm elections, the Democrats are concerned about a certain figure's presence in the electoral campaign who could make them lose their fight against the Republicans for control of the Senate (the House of Representatives is firmly in the hands of the GOP): that man is Barack Obama.

The president's popularity rating is so low that the heads of his party believe it could be enough to swing the balance in favor of the Grand Old Party. The Republicans smell victory. Up until a few months ago, they seemed headed toward certain defeat. Instead, they are now contemplating the opposite – thanks to Obama.

This is not the first time this has happened. In fact, the unwritten rule of midterm elections is precisely this: If there is a Democrat in the White House, it's better to have a Republican Congress, and vice versa. It is called the balance of powers. Capitol Hill uses its power of checks and balances to keep the president from doing whatever he wants.

However, there are certain elections that go beyond this traditional electoral tendency, where the level of satisfaction with the White House's tenant ends up determining the defeat or victory of one of the two parties.

Will this happen in 2014? The Republicans think so, based on their experience in 2006, when they lost the elections. George W. Bush was president and was at his lowest satisfaction level with Americans – 37 percent. The economic crisis had not yet begun, even though the first signs were beginning to show, but America was already tired of the wars in Afghanistan and Iraq.

This terrible record will only be broken by one other president. Who? That's right, you guessed it: Barack Obama, whose work has only received a 42 percent approval rating from Americans. And to think that he has regained ground – a year ago, it dropped to 39 percent.

In 2006, the Republicans lost six seats in the Senate, thereby handing "victory" over to the Democrats. The defeats all came from undecided states, those contested between the two parties. What was the deciding factor? All the analysts agree: it was called Bush.

And yet, the president had been reelected barely two years before; he was the first Republican to earn a second mandate since the time of Ronald Reagan, in what seemed to be an electoral walk in the park – the other candidate was John Kerry. Two years ago, Obama also won with relative ease against Mitt Romney, but 24 months later he finds himself in an unprecedented credibility crisis.

Notwithstanding the positive employment figures, Americans are not happy with the president's actions. They don't give him full marks for economic policy, and fail him on foreign policy. The hesitations, the assessment errors, the return of the terrorist threat partly thanks to mistakes made by the White House have – to a great extent – hacked away at his satisfaction rating. Now it has hit rock bottom. And thus, paradoxically, Barack Obama could become an extra weapon in the Republican Party's arsenal. Who would have ever predicted it two years ago?