Editor's note: This story has been updated throughout.

U.S. Rep. Beto O'Rourke, an El Paso Democrat, told The Texas Tribune he is considering running for the U.S. Senate.

"I am," the sophomore congressman said when Tribune CEO Evan Smith asked if O'Rourke is thinking about running for Senate in 2018 or 2020.

U.S. Sen. Ted Cruz is up for re-election in 2018, while John Cornyn, the U.S. Senate majority whip, will be up for re-election and a fourth term in 2020.

"Am I looking at one of those two races? Yes," O'Rourke said Friday, but he declined to specify whether he would challenge Cornyn or Cruz.

U.S. Rep. Joaquin Castro, who came to Congress in the same class as O'Rourke, is also mentioned frequently as a potential Democratic Senate contender. Only three months ago, Texans at the Democratic National Convention struggled to name a challenger to Cruz.

O'Rourke is a fierce advocate for term limits. So much so that he has repeatedly promised to leave office after four terms. That would put the end of his U.S. House career in 2021.

It is still an open question whether Democrats can mount a statewide campaign in Texas, where they haven't won a statewide race since 1994. But O'Rourke is no stranger to uphill challenges: He ousted long-term U.S. Rep. Silvestre Reyes, a fellow Democrat, in 2012.

In Washington, O'Rourke is viewed as young, liberal and an independent player within his party's caucus in the U.S. House.

The El Paso Democrat also has a knack for drawing national attention. Last summer, his Facebook page went viral as he live-streamed an impromptu U.S. House chamber "sit-in" for gun control from his iPhone. For hours, he broadcasted the events from the House floor, switching out batteries, to the point that when the protest ended, he joked about hand injuries.

The single most consequential factor in any Senate candidacy is an ability to fundraise. In his time running congressional campaigns, O'Rourke proved able but not overly dominant at the task.

Typically, he has brought in in the mid-six figures for his re-election. He topped out in his challenge to Reyes with about $700,000 raised.

A seasoned Democratic Senate campaign operative not authorized to speak on the record projected on Friday that O'Rourke — or any Democratic candidate — would need to raise $30 million to run a “barebones” campaign in Texas. A robust campaign? $50 million. That is for the candidate's campaign alone, before outside groups blanket the airwaves with tens of millions of dollars of negative ads.

For context, the New Hampshire Senate race that will wind down on Tuesday collectively cost campaigns, super PACS and party committees an estimated $100 million and only included one major media market: Boston. Likewise, the current race for the U.S. Senate seat in Pennsylvania between Republican incumbent Pat Toomey and Democrat Katie McGinty has cost well over $100 million.

Texas is far larger than both states in geographic size and population.

O'Rourke's family has significant financial resources. His father-in-law is a wealthy El Paso developer named Bill Sanders. And O'Rourke's financial disclosure forms show he is a millionaire in his own right, but probably could not personally self-fund to the tune of tens of millions of dollars.

There is also another political factor: More so than almost any other public office, the national parties try their best to control the outcomes of Senate primary contests.

Should O'Rourke have a primary rival and national Democrats see potential in picking off Texas, it is likely Democratic senators — and their campaign arm, the Democratic Senatorial Campaign Committee — will play favorites.

O’Rourke, however, may not pay attention to party leadership. That is, after all, how he got to Washington in the first place.

The other issue, more immediately, is political climate.

The consensus at this year's Democratic National Convention in Philadelphia was Democrats' best shot at the Senate seat in 2018 was if Donald Trump won the presidency. All Democrats interviewed said electing Clinton was paramount, but they did concede that historical patterns hold up, a Clinton presidency would set off a 2018 midterm backlash against Democrats nationally.

As for Republicans, they greeted the news of an O'Rourke run with a shrug. Texas Republicans confidently and continually brush off discussion that the state will elect a Democratic senator any time soon. Ron Nehring, a California-based spokesman for Cruz's presidential campaign, echoed that sentiment on Twitter with a single word: "Yawn."

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