This weakens the argument, because it undermines the columnist’s assumption that banning polls in the week before an election would reduce their impact on voters. If everyone has already decided how to vote based on earlier polls, then the last week doesn’t make a difference.

This does not weaken the argument, because we can’t assume that all election races will be uneven and so not decided by polls. If it’s still possible for even elections to be unduly influenced by poll results, the author’s argument is unharmed.

This does not weaken the argument. In fact, this just backs up the columnist’s point that polls can influence election results by providing a specific example of how this takes place.

This does not weaken the argument—it actually underscores the importance of last-minute polls, and thus affirms the columnist’s assumption that those polls make a difference.

This does not weaken the argument, because the columnist isn’t claiming that a ban would result in overall better informed citizens. This also doesn’t say that voters living under such a ban are any worse informed—and even if it did, we wouldn’t know if the ban was the cause.