If the duty of the selection of the President was given to Congress, how might the presidency be compromised?
The President sits at the head of the executive branch, whereas Congress comprises the legislative branch. If Congress was responsible for choosing the President, it could be argued that he would be beholden to that body, and would be guided by the whims of whichever party controlled it. This would compromise the system of checks and balances that was established in the Constitution. Of course, in the event that no presidential candidate receives a majority of electoral votes, the task of choosing the President falls to the House of Representatives. This has only happened twice, in the election of 1800, and the election of 1824. The political horsetrading and accusations of corruption that accompanied both elections, especially the 1824 election, also provides a strong case against Congress choosing the President except in these extreme cases.