Senator Elizabeth Warren has made her first moves on her 2020 campaign trail, by announcing a four-city visit to the crucial state of Iowa.

Warren announced on Tuesday she will visit the cities of Des Moines, Council Bluffs, Storm Lake, and Sioux City.

They will be her first public appearances since announcing on Monday that she had set up an exploratory committee for a presidential campaign.

The events include three open meetings at a large bar, a theater, and a community centre. The fourth, in Storm Lake, is described as a roundtable discussion

The existence of the committee does not mean she is definitely running in 2020, but it is the first step toward staking a claim to be the Democrats' leading candidate.

Another popular Democrat Senator, Beto O'Rourke, met with Barack Obama in his Washington offices in November, suggesting he too may have ambitions in 2020.

Elizabeth Warren is the highest-profile Democrat name so far to pursue a formal presidential run. AP/Charles Krupa

Iowa is significant for presidential wannabes as it changes its party allegiance all the time, and is widely known as a pivotal swing state in tight election races.

It voted for Republicans Donald Trump and George W. Bush in 2016 and 2004, but in-between, voted for Obama and the Democrats (in 2008 and 2012.)

Iowa hosts the first presidential primary election on February 3, 2020. In the final presidential vote, Iowa has been on the side of the winning candidate in 2016, 2012, 2008, and 2004.

Read more: Meet the 2020 presidential contenders who are poised to start campaigning right away in 2019

Warren, the highest-profile Democrat so far to hint at running in 2020, made the first step towards declaring her formal candidacy by sharing a video on Twitter and launching a website that went live on Monday morning.

In the video she described her vision of defending the middle class, which characterised as being "under attack."

Here's the full video:

President Trump responded to Warren's video on Fox News' "All-American New Year" special on Monday.

When asked whether Warren had a shot, he said: "Well, that I don't know. You'd have to ask her psychiatrist."

The presidential exploratory committee means Warren can start receiving donations, travel around the country whipping up support, and test the waters, before deciding whether to officially declare her intention to run.

Warren will speak on Friday in Council Bluffs, and will visit Sioux City, Storm Lake and Des Moines on Saturday.