The answer is:
Appointment power.
Some of the goals of the president’s power of appointment is to shape foreign and domestic policy as well as the federal judiciary in a particular ideological way by using his powers to appoint the most qualified representatives to accomplish said objective.
This is a huge responsibility, before taking office, the president and his transition team must appoint people to more than 6,000 federal positions. Many, but not all, of these positions at the highest levels are appointed by the president with the advice and consent of the United States Senate. The senate must confirm qualified people for these positions in order to have a successful and healthy democracy. The senate must also help the president confirmpersons to fill federal judicial vacancies, including federal judges, such as members of the United States courts of appeals and the U.S. Supreme Court.
The nominations for Judges require Senate confirmation because this can help shape a president’s stance on certain issues. There are those who believe the Constitution is a limited document. It lays the framework and the rules and that's all. And by appointing the right judges a president may exercise the law a certain way. One such example trending now is whether said judge is either pro-choice or not.
In any case, over the course of the last 240 years or so, the powers of the President have expanded far beyond what the constitution probably envisioned. And that’s how presidents now have the right to exercise their powers.