Many American presidents in the 19th century were born in poor families. They spent their childhood in little wooden rooms. They got little education. Washington and Lincoln, for example, never went to school and they taught themselves. Lincoln once did jobs of a worker, shopkeeper and post in his early years.
A large number of American presidents had experiences in the army. The two best known were Ulysses Grant and Dwight Eisenhower. Grant was a general in the American Civil War and Eisenhower was a hero in the Second World War. It happened that they graduated from the same school— West Point Military Academy (西点军校). One may be surprised to learn that both of them did not do well in the school. Eisenhower, for example, was once fined because he broke the roles of the school.
The jobs of the US president are tiring. He must keep an eye on anything important which happens both at home and abroad. Every day, a lot of work waits for him to do and he has to make many important decisions. When Franklin Roosevelt was a child, he was once brought to visit President Taft. The old president said to him, "When you grow up you should not be the president. It’s a tiring job.\
In the third paragraph, "keep an eye on" means "______".