Presidents' reliance on advisors rather than on members of their Cabinet affect the process of checks and balances because C) political advisors are not subject to confirmation by Congress.
According to the Appoitments Act of the Constitution, the Senate must be consulted and must confirm appointments made by the president to certain charges (ambassadors, federal judges, Cabinet members). However, the political advisors are not included in that list and the President can name them without the intervention of the Senate.
This weakens the process of checks and balances that relies on the control that each branch of the Government have on the others. If the Senate does not intervene in the appointment of key officials, its influence on political issues is lessened.