Sorry, but forcing idiot politicians to show the electorate how good a job they are doing would basically put them in a continuous election/campaigning cycle (because that is effectively their job performance review, and the Congress/Senate campaign cycle lasts for at least 6-9 months as it is), meaning that they would do even less useful work than they do now.
The fact that you are right about the attention span of voters being too short to remember anything that has not happened in the last week (not sure if I am being too generous there, sometimes I think it is much shorter than that) does not mean that the election/performance review cycle should be shortened, it means that the electorate actually need to put some effort into considering who to vote for.
Too hard? Then the electorate are too lazy/stupid/incompetent, and they get the candidate they deserve. Remember, these politicians are supposed to be the best representatives of the people in their constituency. So if the electorate are lazy, then the politician has to be only slightly less lazy.
Remember, when being chased by zombies or cannibals, you do not have to be faster than the zombies or cannibals, you just have to be faster than the dumb schmuck next to you, so that they catch him, and you get away. On in the case of politicians, they only have to be slightly better than the other guy, who has to be only slightly better than anyone else.