The two leading Democratic presidential candidates say they wouldn't be intimidated by former New York Mayor Michael Bloomberg launching a third-party independent campaign.
Bloomberg said last week he is considering getting into the race.
The Democrat-turned-Republican-turned-independent has liberal views on such issues as gun control, abortion rights, and immigration. He would most likely take votes away from the Democratic nominee in the November election.
Democratic front-runner Hillary Clinton appeared unconcerned about a Bloomberg run, telling NBC television's Meet the Press Sunday "The way I read what he said is if I didn't get the nomination, he might consider [running]. Well, I'm going to relieve him if that and get the nomination so he doesn't have to."
Democratic candidate Bernie Sanders says he is not happy over the possibility of another wealthy presidential contender.
Bloomberg, like Republican candidate Donald Trump, is a billionaire - having earned his fortune in the media.
"This is not what, to my view, American democracy is supposed to be about, a contest between billionaires. If that takes place, I am confident that we will win it," Sanders said on ABC's This Week program.
This is the last week candidates have to campaign before the February 1 Iowa caucuses - the first events in which voters actually make their choices.
The latest polls show Democrats Clinton and Sanders just about tied, with former Maryland governor Martin O'Malley far behind.
Most polls give Republican Trump a large lead over his rivals. But one survey by CBS News/YouGov shows him with just a five percent lead over Texas Senator Ted Cruz.