Answer:
C: Democrats had won a large majority in Congress.
Step-by-step explanation:
The reason President Roosevelt was able to enact new reforms during the Second New Deal was primarily due to option C: Democrats had won a large majority in Congress. In the 1936 elections, the Democratic Party secured significant victories, gaining a substantial majority in both the House of Representatives and the Senate. This shift in Congress allowed Roosevelt to pass legislation and implement his reform agenda more effectively. With a supportive majority, Roosevelt had the political leverage to push through his proposals and advance his policy goals.