(CNN)Once supportive Senate colleagues -- they stood in for each other during their respective marathon Senate speeches -- soon-to-be rivals Sens. Rand Paul and Ted Cruz are decidedly less chummy these days.
Rand Paul knocks soon-to-be rival Ted Cruz
Paul made it clear Monday night he plans on waging a debate against his fellow tea party Republican, Cruz, who on Monday declared himself a presidential candidate.
"Right now, I'm the only one that beats Hillary Clinton in certain purple states," Paul said on Fox News' "The Kelly File," talking about recent polls. "There will be a lot of conservatives. Ted Cruz is a conservative, but it also goes to winability. And people will have to make a decision: Which is the Republican that can not only excite the base but can also bring new people into the party without giving up principles?"
The Kentucky Republican, who's expected to announce his own presidential bid on April 7, said he was "glad" to see Liberty University students wearing t-shirts in support of his own all-but-declared candidacy, when Cruz made his announcement.
"I guess what makes us different is probably our approach to how we would make the party bigger," Paul said, referring to himself and Cruz. "I'm a big believer that you should stand on principle ... but I also think we should take those principles and try to bring in new people with them."
For Paul, that means "not just throwing out red meat, but actually throwing out something intellectually enticing to people who haven't been listening to our message before."
Cruz has rocketed to the national spotlight in two and a half years since winning election to the Senate in 2012, in part because of his unabashed efforts to take down Obamacare. He's become a favorite among tea party circles, and his campaign strategy involves targeting the more libertarian wing of the party as well.
"Instead of a government that seizes your emails and your cell phones, imagine a federal government that protected the privacy rights of every American," Cruz said during his speech Monday.