The executive branch is able to influence the actions of the legislative branch by the veto power of the President.
The veto power is the power of the President not to sign into law legislation made in Congress. When the President vetoes a bill, it is sent back to Congress without becoming a law. The veto right was established to prevent the legislative branch from becoming to powerful. It is part of the 'check and balances' system of separation of powers.
The executive branch is able to influence the actions of the judicial branch with the appointment of judges.
On the federal level, the president appoints judges and Supreme Court Justices. The Senat confirms or denies the appointments later but the power of the president here is great. The judges are nominated for life, it means that the president's ability to influence the federal courts lasts much longer than that particular president's term of office.