I think this is a nonstandard use of "chalk up", and here it simply means to write or create. The politicians created laws that benefited themselves. Normally, "chalk up: means: 1) to give as the reason for something. "I chalked up his failure to his inexperience" or "We chalked up the poor attendance to the bad weather". 2) to achieve something. "The team has chalked up victory after victory this season" or "She chalked up more sales this quarter than any other employee".