The legacy of the 2011 debt ceiling fight is the biggest issue the next president will face on day one

Five years ago on Tuesday, President Barack Obama signed into law what Todd Harrison, the director of defense budget analysis at the Center for Strategic and International Studies, says will be the biggest challenge for the incoming administration.

The Budget Control Act of 2011 (BCA).

In short, after taking the highest office in the land, the 45th President of the United States will have less than 300 days to strike a budget deal with Congress or see America's defense funds slashed.

Here's what you need to know about the BCA and America's arms budget.