Not really, jj, as far as in Presidential elections. The examples of third party candidates spoiling the chances of one party or the other have favored the GOP. In 1968 George Wallace ran as a Dem and took millions of votes from Humphrey, who lost. Then in 2000, Ralph Nader was widely viewed as having taken thousands of votes from Gore in Florida, the vote re-count state. Post election pollsters found that 60% of Nader's voters were Dems.
In state and local elections, 3rd party candidates can help or hurt both parties. The Dems in AL are hoping a 3rd party candidate enters their special election to replace Session's seat in the US Senate, to take some votes away from Roy Moore.