Though no firebrand, Warner has not shied way from joining the fight against the president.
He's the vice chairman of the Senate Select Committee on Intelligence, which is continuing to investigate whether President Donald Trump's campaign colluded with Russian operatives during the 2016 presidential election.
He took on Trump by co-sponsoring bipartisan legislation against the administration's import tariffs on U.S. allies Mexico, Canada and the European Union. The bill, also sponsored by Republican Sen. Bob Corker of Tennessee, would require the White House to seek congressional approval before issuing tariffs for national security interests.
Warner faced off with the Commerce Department on its decision to lift a ban on conducting business with ZTE, a Chinese telecommunications equipment manufacturer that was accused of breaking international sanctions on Iran and North Korea in 2017.
However, on Thursday, Commerce Secretary Wilbur Ross announced on CNBC that it had struck a deal with ZTE to end the sanctions.
Donors are looking at his ability to stand up to the Trump administration as a potential platform for him to run on in 2020 on top of his moderate economic views if he were to jump into the race, sources say.
A national Morning Consultant poll of the most popular senators taken in April shows Warner with 49 percent approval and 30 percent disapproval. The poll shows Sanders is still the most popular among Democrats, whom he caucuses with.
Correction: Sen. Bernie Sanders is an independent from Vermont. An earlier version misstated his political affiliation.