Among the most effective is running advertisements attacking an opponent's personality, record, or opinion.
And last year, business groups, led by health-insurance companies, poured about $4 million into advertisements attacking him.
Republicans have responded with advertisements attacking Democrats for raising taxes and as being weak on national security.
The advertisements attack the main Democratic bill by name, but provide justification - and political cover - for senators to vote against any patients' rights legislation.
These advertisements appeared in the closing weeks of the election and attacked his Democratic opponent as an out-of-state liberal.
He countenanced broadcasting $1 million worth of advertisements attacking 20 Democratic lawmakers who opposed him.
The other advertisement, attacking Mr. Clinton on the budget, is a more customary example of issue advocacy.
Since the advertisement also attacks Mr. Dole on education, it could eventually be broadcast more broadly.
One reason: her advertisements bluntly attack her competitors as charging customers wasteful fees.
The advertisements attack the senator's support for a bill that would sharply increase the number of visas available for companies to bring in foreign high-technology workers.