Conservative radio show host and former lawmaker Joe Walsh has become the second man to challenge President Donald Trump for the Republican Party's 2020 White House nomination.
"The country is sick of this guy's tantrum [sic] - he's a child," Mr Walsh, 57, told ABC's This Week, in what is seen as a long-shot challenge.
President Trump made no immediate public comment on the news.
Both men now face an uphill battle to take over a Republican Party that has been refashioned in Mr Trump's image.
No sitting president in the modern era has lost the race to be a nominee for their own party.
But both Jimmy Carter in 1980 and George Bush Snr in 1992 faced strong challenges that foreshadowed difficult presidential elections they would lose.
What else did Joe Walsh say?
"I'm running because he's unfit - somebody needs to step up and there needs to be an alternative," he told ABC.
Mr Walsh was elected to the House of Representatives from Illinois in 2020, riding the Tea Party wave.
The Tea Party movement is a conservative group within the Republican Party.
Who will take on Trump in 2020?
Election day is still more than a year away but the race to become the Democratic challenger to Mr Trump is already well underway.
Joe Biden and Bernie Sanders have thrown their hats into the ring, but most of the other candidates are relatively unknown outside the Washington DC bubble.
"The country is sick of this guy's tantrum [sic] - he's a child," Mr Walsh, 57, told ABC's This Week, in what is seen as a long-shot challenge.
President Trump made no immediate public comment on the news.
Both men now face an uphill battle to take over a Republican Party that has been refashioned in Mr Trump's image.
No sitting president in the modern era has lost the race to be a nominee for their own party.
But both Jimmy Carter in 1980 and George Bush Snr in 1992 faced strong challenges that foreshadowed difficult presidential elections they would lose.
What else did Joe Walsh say?
"I'm running because he's unfit - somebody needs to step up and there needs to be an alternative," he told ABC.
Mr Walsh was elected to the House of Representatives from Illinois in 2020, riding the Tea Party wave.
The Tea Party movement is a conservative group within the Republican Party.
Who will take on Trump in 2020?
Election day is still more than a year away but the race to become the Democratic challenger to Mr Trump is already well underway.
Joe Biden and Bernie Sanders have thrown their hats into the ring, but most of the other candidates are relatively unknown outside the Washington DC bubble.