The shift in power from Congress to the executive branch over domestic policy was primarily driven by deregulation under Reagan, the growth of the federal bureaucracy, and the increase in the national debt.
The most significant factor contributing to the shift in power from Congress to the executive branch over matters of domestic policy is the wave of deregulation that began with President Reagan. Reagan's policies aimed at reducing government intervention in the economy, leading to a stronger executive role in shaping domestic policy.
Additionally, the growth of the federal bureaucracy during the 20th century played a key role in consolidating power within the executive branch. The expansion of bureaucratic agencies granted the president more authority in implementing and overseeing policy initiatives.
Furthermore, the rise of the national debt over the past several decades has also shifted power towards the executive branch. Increasing debt levels have often necessitated executive decision-making on fiscal matters, giving presidents more influence over domestic policy.