More than once, readers have asked me, "If Ford's (NYSE:F) Fusion sedan is so popular, why hasn't it beaten Toyota's (NYSE:TM) Camry yet?" While the Fusion has made a big dent in the Camry's market share this year, its total sales are still well behind the Camry, which still reigns as America's best-selling car.

Why? The answer is simple, if surprising: The factory that makes the Fusion can't keep up with demand, even though it's running around the clock. Ford hasn't been able to make enough Fusions to catch Toyota -- or Honda's (NYSE:HMC) Accord, for that matter.

Ford has been selling all the Fusions it can make -- and soon, it'll be able to make a whole lot more. Photo credit: Ford Motor Co.

But soon, a second Ford factory will begin making Fusions, and Ford's total production capacity will be closer to Toyota's and Honda's. That means it's showtime for the Fusion, but there's a big catch: At the same time, Toyota is making its own big moves to pump the Camry's sales back up.

In this video, Fool contributor John Rosevear looks at the state of the battle to be America's best-selling car and how the increased supply of Fusions is likely to affect both Ford and Toyota.