For Ted Cruz, the single biggest obstacle to winning the Republican presidential nomination may not be outsider candidates Donald Trump or Ben Carson, but his fellow first-term senator, Marco Rubio.

After strong debate performances, Cruz and Rubio — both 44-year-old Cuban Americans — saw their poll numbers rise and interest from donors jump. They are now locked in a third-place tie, according to a national Los Angeles Times poll ahead of Tuesday’s debate in Milwaukee. As a result, Cruz and his allies have begun zeroing in on Rubio.

“As I look at the race, historically, there have been two major lanes in the Republican primary. There’s been a moderate lane and a conservative lane,” Cruz told CNN on Thursday. “Marco is certainly formidable in that lane. I think the Jeb [Bush] campaign seems to view Marco as his biggest threat in the moderate lane.”

Read the article “Ted Cruz Sets Sights on ‘Moderate’ Marco Rubio” on bloomberg.com.