The problem of the expansion of executive authority in the Presidential Government System: Presidential Decrees in light of Constitutional Court decisions

The Presidential Government System established by Constitutional Amendment No. 6771 has granted the executive branch the authority to enact substantive regulations through Presidential Decrees. This situation has raised a fundamental issue regarding the constitutional limits and oversight of the administration. This study evaluates the assumption that the expansion of executive authority has been achieved through Presidential Decrees. The main objective of the thesis is to reveal this trend of expansion and its constitutional consequences. In line with the stated objective, the relevant case law of the Constitutional Court has been systematically examined using doctrinal analysis methods. The scope of the research consists of Presidential Decrees issued during the ordinary period from 2018, when the Presidential Government System came into force, to the present day, and the Constitutional Court's case law related to these decrees. The original value of the study lies in bringing together the scattered case law of the Constitutional Court around the main thesis of the "tendency to expand" of the executive branch, offering a comprehensive, systematic, and evidence-based synthesis that is lacking in the literature. The main findings of the thesis show that the expansion of the executive branch is a multi-layered trend. It has been determined that the executive branch has structurally expanded by creating positions, intervening in personnel regulations, and establishing new administrative structures through Presidential Decrees, but that this expansion has been partially limited by the Constitutional Court (constitutional autonomies, financial rights, and fundamental status law). It has also been revealed that the executive branch has attempted to expand functionally by using this structural power to interfere with the legislature's budgetary rights and areas that must be regulated exclusively by law, but that these attempts have been largely halted under the supervision of the Constitutional Court (prohibition on generating public revenue, fundamental rights, interference with the text of the law). It has been concluded that the dual expansion trend undermines the principle of legal certainty, the balance of separation of powers, and oversight mechanisms through methods such as delegating primary regulation to regulations and using ambiguous norms. In light of these findings, the thesis's main proposal is to restore constitutional balance and oversight mechanisms by clarifying the constitutional limits of the President's authority to issue decrees, strengthening the guarantees of provisions such as Article 128 of the Constitution, which regulates the public personnel regime, and enhancing the oversight powers of the legislature.