WASHINGTON – U.S. Rep. Beto O'Rourke, a Democrat and ex-punk rocker who pulled a stunning upset to win his House seat six years ago, plans to declare his candidacy on Friday for the Senate seat held by Ted Cruz, according to Democratic sources in Texas.

O'Rourke's fledgling campaign has scheduled an announcement on Friday in El Paso, his hometown. He has traveled heavily in Texas over the last three months making contacts, barely concealing his political plans.

"I'm very moved to do it," O'Rourke, 44, said in an interview earlier this month, adding that he had reached the "emotional decision" about his candidacy.

Campaign aides declined to confirm that he will enter the 2018 Senate race.

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U.S. Rep. Joaquin Castro, D-San Antonio, is the only other high-profile Democrat who has expressed interest in running against Cruz. Castro, 42, who has climbed the House ranks more swiftly than O'Rourke and may see himself as having more to lose, said recently he will announce his decision next month.

O'Rourke is a three-term congressman and, as a rare term-limits supporter among Democrats, likely would have been around for just one additional term in the House. He drew thousands of livestream followers earlier this month by making a cross-country, bipartisan auto journey from San Antonio to Washington with U.S. Rep. Will Hurd, R-San Antonio, after a snowstorm canceled flights.

For any Democrat, a challenge of Cruz might be considered decidedly uphill given the Texas senator's speedy rise in politics and national fundraising sources. Cruz, 46, is serving only his initial term in the Senate but in 2016 he was a finalist in the GOP primary race, emerging as the last contestant vanquished by Donald Trump.

A Cruz-O'Rourke race would offer a stark ideological contrast; a staunch conservative and self-described Constitutionalist versus an unabashed liberal who supports recreational marijuana.

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Cruz is a lawyer, O'Rourke a businessman in the technology industry and a musician who played in three punk rock bands during and after his college years at Columbia University.

A contest between Cruz and O'Rourke also would offer dramatic differences on border issues. Cruz has supported Trump's hard-edged immigration policies while O'Rourke has positioned himself as a friend of immigrants, trumpeting the economic and cultural benefits of a close relationship with Mexico.

"Beto brings a fresh approach, a new face, and is someone who is able to connect with Texans across the board," said Matt Angle, executive director of the Lone Star Project, an organization that promotes Democrats in Texas.

Angle acknowledged that Democrats have their work cut out for them in trying to unseat Cruz, a tea party backed conservative who built up a national conservative following in a White House bid last year.

"The challenge will be for Beto or anyone else running in a Senate race againt Cruz to have the resources and the megaphone big enough to tell their story statewide," he said.

Given Cruz's profile as a national movement conservative leader, the race is likely to attract nationwide attention and money.

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The Cruz campaign declined comment.

Robert Francis O'Rourke (he has been called Beto since he was a child) secured his far West Texas by winning the 2012 Democratic primary primary challenge of Silvestre Reyes, an eight-term incumbent and former Border Patrol agent.

O'Rourke has been in minority for all of House career with little opportunity to get his name attached to splashy legislation. As a member of the Veterans and Armed Services committees, he has devoted much of his energy to veterans' issues, especially issues related to the mental health of those who have served.

Scroll through the gallery above for the things you need to know about the Democrat who is taking on Ted Cruz.