The problem current changes overtime because different issues tend to need attention at various times. The problem current can flow through at any moment and can be almost anything. It can be an old problem, new problem that looks unsolvable and a small everyday routine problem. A president can decide how they want to deal or not to deal with the problem. For example, in 1969 Nixon concentrated on foreign problems, detente with the soviets, Vietnam War, and a new China policy while ignoring domestic policy.
Problems can also appear as fast as they can disappear.
The civil rights problem appeared very hot during the 60's then disappeared on till the late 80's when it was taken up again. The most critical question one needs to ask when dealing with the problem current is why are some problems addressed and others are ignored by the president. Light states that theoretically, presidents can assign specific values to every problem in the policy stream, then choose the problem with the highest return. But, realistically they can only guess the rough rewards of one problem over another either through public opinion or their own political instinct. After a problem has been chosen or ignored the president still must deal with the solutions.