In the race for the Democratic presidential nomination, U.S. Sen. Elizabeth Warren is in a three-way tie at the top with Vermont Sen. Bernie Sanders and former Vice President Joe Biden of Delaware, according to new poll results.

Warren and Sanders both counted increased support among registered Democrats and Democrat-leaning voters in the Monmouth University Poll released on Monday, which showed that Biden's big lead in Monmouth's June poll had evaporated.

Biden had 32 percent support in the June poll, but was the choice of 19 percent in the latest poll, which was conducted by phone from August 16-20 with 800 adults in the United States and is based on 298 registered voters who identified as Democrats or leaning toward the Democratic Party. The poll's margin of error is plus or minus 5.7 percentage points.

Warren and Biden were each at 20 percent in the latest poll, up from 15 percent and 14 percent, respectively, in the June poll.

"The main takeaway from this poll is that the Democratic race has become volatile. Liberal voters are starting to cast about for a candidate they can identify with," Patrick Murray, director of the independent Monmouth University Polling Institute, said in a statement. "Moderate voters, who have been paying less attention, seem to be expressing doubts about Biden. But they are swinging more toward one of the left-leaning contenders with high name recognition rather than toward a lesser known candidate who might be more in line with them politically."

As Warren eyes the November 2020 presidential ballot, U.S. Sen. Ed Markey may also have a tougher fight on his hands next year, with U.S. Rep. Joe Kennedy newly touting his interest in the seat Markey holds and support for his potential run.