(CNN) The top Democratic candidates best President Donald Trump in national head-to-head matchups, according to a new poll from Quinnipiac University out Tuesday.

With the general election still more than a year away, former Vice President Joe Biden leads the pack, with the largest advantage over Trump. The poll shows 53% of voters said they would support Biden and 40% said Trump. Biden and Trump held side-by-side events in Iowa on Tuesday, both using their platforms to insult the other one. Biden called Trump an "existential threat" to the country and Trump said Biden was a "dummy."

The gap is smaller but still a distinct advantage for Sens. Bernie Sanders (up 9 percentage points), Kamala Harris (+8) and Elizabeth Warren (+7). Others candidates, such as Sen. Cory Booker and Mayor Pete Buttigieg, scrape by the margin of error, leading Trump by 5 percentage points each.

Biden holds a 30-point lead among independents: 58% back him, vs. 28% for Trump. Trump's best showing among independents in this poll is 34% against Warren.

Most of the Democratic candidates took to Iowa last weekend, with primary season off to the races. Trump has a few primary challengers, but no polls have shown them as seriously competitive with him.

Read More