Final answer:
Obama's power to implement his agenda waned when faced with resistance from a Republican-controlled House, increased use of filibusters, and slow judicial confirmations. It further declined with economic concerns, rising federal debt, and unmet promises contributing to a decrease in support from his left-leaning constituency.
Step-by-step explanation:
President Barack Obama's power began to wane partially during his first term, with significant difficulties during his second term. Despite winning the 2008 election with optimism for change and a strong voter mandate, Obama faced intense political gridlock and resistance from Republicans, who retained control of the House of Representatives. This was evidenced by an increase in filibusters, and an unwillingness to vote on key legislation like the 2012 "jobs bill," and the slow confirmation of judicial nominations. As his second term progressed, challenges such as the economic health concerns, federal debt, and unfulfilled promises further eroded support from some constituencies, showcasing the difficulty in maintaining presidential power amidst a polarized political climate.