Democrats have their sights set on a major Republican after Doug Jones' upset win in Alabama - Ted Cruz

AP Photo/Carolyn Kaster

Sen. Ted Cruz on Capitol Hill.

• Democrats see top GOP Sen. Ted Cruz as uniquely vulnerable in the wake of Doug Jones's upset win in Alabama.
• Cruz's favorability ratings are lowers than Republican Roy Moore's unfavorable ratings.

Despite Alabama Senate candidate Roy Moore's numerous flaws, Democrat Doug Jones's victory over the former judge Tuesday night caught many political observers by surprise.

But for other Democrats, it signaled consequences for Republicans up for reelection, including a longtime Democratic foe: Sen. Ted Cruz. 

"Be afraid, @tedcruz. Be very afraid," former Housing and Urban Development Julian Castro said in a tweet.

Some Democrats believe Cruz's low popularity in Texas has made him uniquely vulnerable to a Democratic challenger in 2018. 

Observers like Vox's Matt Yglesias noted that Cruz's favorable ratings were actually lower than Moore's in some recent polls. 

Democrats in the state also saw an opportunity in Moore's defeat. 

Beto O'Rourke, seen as the Democratic frontrunner who will likely challenge Cruz next November, sent an email to supporters on Tuesday fundraising off of Jones' win.

"If you weren't sure if our campaign to take on Ted Cruz was possible, you have to know it is now," the email said. "Next stop, Texas 2018."

O'Rourke's campaign also shared a tweet of Cruz saying Moore, who has been accused of sexual misconduct with teenagers, should be seated in the Senate if he won the election. 

Democrats have not won a Senate race in Texas in decades, and are likely face an uphill battle even in a potential wave election.

President Donald Trump won Texas by a margin of nine points over Democratic nominee Hillary Clinton in 2016. That was seven points lower than Republican Mitt Romney's margin of victory over Democrat Barack Obama in the state in 2012, but was slightly lower than Cruz's margin-of-victory over Democratic nominee Paul Sadler in the Senate race that same year. 

Nonetheless, following Jones' victory, many Democratic strategists and supporters immediately called for greater attention to the race in Texas.