Final answer:
Option (a), The trend is troubling as it concentrates power by bypassing the system of checks and balances when presidents unilaterally engage in armed conflicts without seeking a Congress declaration of war, shifting the balance of power towards the executive branch.
Step-by-step explanation:
The trend of modern presidents engaging in armed conflicts without seeking a formal declaration of war by Congress is considered by some to be a troubling use of presidential power because it bypasses the system of checks and balances, concentrating power in the executive branch. This practice, which grew especially after the passage of the War Powers Resolution in 1973, allows presidents to act unilaterally for sixty days before getting congressional authorization, often resulting in military engagements without a formal declaration of war.
Despite congressional powers to amend, oversee, and manage the budget for war efforts, the need for rapid decision-making and the complexities of modern international relations have contributed to the president's continued dominancy in foreign affairs.