(CNN) The next 100 days will be critical to understanding whether President Donald Trump will win a second term in office. His approval rating has been consistently low during his first term. Yet his supporters could always point out that approval ratings before an election year have not historically been correlated with reelection success.

But by mid-March of an election year, approval ratings, though, become more predictive. Presidents with low approval ratings in mid-March of an election year tend to lose, while those with strong approval ratings tend to win in blowouts and those with middling approval ratings usually win by small margins.

Let's start with where Trump is right now : an approval rating in the low 40s. Since World War II, two presidents have had an approval rating at or below 45% in mid-March of an election year. George H.W. Bush had an approval rating at 39%, while Jimmy Carter's was at 45% and falling fast. Both of them went on to lose reelection by greater than 5 points.

On the opposite end of the spectrum, there have been five presidents with an approval rating of 55% or above. There was Bill Clinton at 55%, Ronald Reagan at 55%, Richard Nixon at 58%, Dwight Eisenhower at 72% and Lyndon Johnson at 80%. All of these presidents won their elections by nine points or greater.

Finally, we have the group of presidents with approval ratings between between 46% and 54%. This includes Gerald Ford at 47%, Barack Obama at 47%, George W. Bush at 49% and Harry Truman at 51%. All of their elections were decided by less than 5 points.