From Bernie Sanders to John Kasich: Potential Trump challengers in 2020

Buoyed by Tuesday's takeover of the US House of Representatives, Democrats can now turn their attention to the 2020 presidential race. 

For the first time since the start of the 2004 campaign, Democrats are entering the cycle without a dominant front-runner. More than two dozen possible contenders have had their names floated or have actively begun exploring their chances. 

President Donald Trump filed for re-election the day he was inaugurated in January 2017, and his popularity with the Republican Party's core supporters means any possible challenge for the party's nomination will be a longshot.

Here are some of the potential contenders in each