You can use what his campaign has paid for and owns and gives you. News clips will need clearance and a fee from the TV station and/or network. Same for newspaper stills.
Screen-capping the other side's commercials to pull shots and quotes from is iffy territory; better ask a lawyer.
This is one of the reasons to pay for a campaign "tracker": he or she does nothing but follow the target everywhere, recording all the time. If a situation comes up where the target person makes a useful quote, you can buy it from the tracker straight away, rather than deal with the TV stations. The tracker's angle may be a little different and framing or sound may not always be as good, but you own the footage free and clear.