In American politics, it is not unusual for a POTUS to have less than a 40% approval rating while in office. It fluctuates. "Majority" approval ratings happen but are rare. Trump is currently at about 42%. Our last POTUS was 48% average. The highest in modern history was actually a terrible President. He had a whopping 70% average approval, but he:
- Started the US involvement in the Vietnam War.
- Planned a sneak attack on another country which failed, and left a mess for 50 years. He caused the whole problem with Cuba, and effectively forced them to align with the USSR, and even snubbed their new leader deliberately by dodging a peace meeting with him.
- Nearly started a thermonuclear war with the only other superpower on earth because he was immature politically and could not untangle a mess he started, nor did he understand military tactics and technology at a high enough level.
- Was heavily into nepotism and privilege by birth. His father was Nazi supporter and a professional criminal at one point. He was the closest America ever came to having a King, and our first fully pre-packaged and sanitized POTUS. This monarchy is still alive even today.
- He did more to accelerate the Cold War than any other President, even though he was not in office long.
So approval ratings don't mean much. In fact, they can be an indicator of a President who says what you want to hear, but is a screw up.
Only 3 Presidents in modern times did not have lower than 40% during their tenure.
Kennedy - Worthless as a leader. A menace to world peace without a clue as to how to deal with people.
Eisenhower - A brilliant organizer and leader.
FDR - A socialist who wanted to dissolve the Supreme Court, hated Negroes (historical) and endorsed segregation in all forms, put his own people in concentration camps without due process, and wanted to be leader for life. He admired Stalin as a leader, and had no problem with the fact Stalin was on the Axis side of WWII until he was attacked by his ally.
So the two out of three of the most popular Presidents were not fit for office.