Why might Caesar's assassins have been unhappy with the long-term results of their actions?

The assassination failed, and Caesar served many more years as leader. After Caesar's death, Augustus expanded the powers of Rome's leader. The assassination prolonged the republic for another hundred years.

The power and influence of the senate increased after the death of Caesar.

After Caesar's death, Augustus expanded the powers of Rome's leader.

Explanation:

The assassination of Julius Caesar precipitated a new civil war by the spoils of power and thus the republican constitutional government was never totally restored. His great-nephew, Caio Octavian, was made his heir in a will. In 27 B. C., the young man would go down in history as Augustus, the first Roman emperor, adopting the title of Caesar and expanded the powers of the leader of Rome.

To protect the republic, the senators killed Julius Caesar, unaware that they would annihilate their political class and cause their own frustrations.

Caesar was named "dictator for life" by the Roman Senate. Some of the senators, such as Gaius Cassius Longinus, Decimus Junius Brutus Albinus, and Marcus Junius Brutus, feared that he would take the Senate power and become king or emperor, so they decided to kill him. They expected the Roman people to support them, which didn't happen.

After Caesar's death, Augustus expanded the powers of Rome's leader, for example by deifing him.