Answer:
Passing campaign finance laws
Step-by-step explanation:
The state government is responsible for registering voters. Each sate has their own laws about what documentation is needed, deadlines, etc.
State/local governments are responsible for orgainizing local polling (or voting) places. Districts are created within a state, county, or city. Based off which district your home falls into, you have a specific location you are able to cast your vote at.
Sates are responsible for counting votes. We see this each election when certian states ((Navada, Florida, Alaska, Pennsylvania, Georgia)) take much longer than other states to tally up votes.
I honest don't KNOW this, but process of elimination tells me that the federal government must be responsible for passing campaign finance laws. And it makes sense.