Hillary Clinton is not the only Democrat seeking the party's nomination in the 2016 White House race but you wouldn't know it from her appearance at a Friday fundraiser in Iowa, where the frontrunner focused exclusively on her GOP opponents -- even though her internal challengers were also in attendance.

The former secretary of state described her presidential campaign as a "deeply personal" quest and promised that she would not allow Republicans to "rip away the progress" she said was made during the Obama administration, the Associated Press reported.

Clinton criticized former Florida Gov. Jeb Bush over his economic policy, made a joke at the expense of Donald Trump's hairstyle and attacked Wisconsin Gov. Scott Walker over his fight with labor unions. But the former New York senator had nothing to say about Vermont Sen. Bernie Sanders, former Maryland Gov. Martin O'Malley, former Virginia Sen. Jim Webb and former Rhode Island Gov. Lincoln Chafee -- all of whom plan to challenge her in the primaries.

"You can see that Democrats are united, we are energized, and we are ready to win this election," Clinton insisted, according to the National Journal. And at least in their speeches at the fundraiser, Sanders, O'Malley, Webb and Chafee followed Clinton's lead and avoided aiming criticism at fellow Democrats.

During an afternoon appearance in Cedar Rapids, however, Sanders dared to question whether Clinton would back the kind of tough regulation on Wall Street that's becoming a rallying call for liberals, the AP noted.

"You'll have to ask Hillary Clinton her views on whether we should break up these large financial institutions; I do," said the Vermont senator -- whom many consider to be the only contender who can hope to mount a serious challenge to the former first lady.

The Clinton campaign has admitted that it considers Sanders to be a legitimate competitor, noting the $15.2 million he has raised in the first three months of the race. That money comes largely from small donors, leading observers to believe that the Vermont lawmaker may fare well in caucus states such as Iowa.