Sen. Ted Cruz, R-Tex., on Monday is expected to announce he's running for president. However well he ends up doing in the Republican primaries, one thing is for sure — the development is terrible news for Sen. Rand Paul's presidential ambitions.

Whatever small chance Paul had in the 2016 presidential race was premised on his ability to reach beyond the core supporters of his father's, by articulating a message that appealed to a broader coalition of Republicans. The biggest opportunity Paul had for growth was with Tea Party voters who would be drawn to his limited government message. The biggest obstacle he had was foreign policy views that are also out of step with many of those voters.

In an ideal world for Paul, he'd try to find a way to assuage the concerns of national security-oriented conservative voters without totally alienating his core supporters. And one way to do that was attack the other candidates for being insufficiently committed to limited government principles. That already difficult task becomes effectively impossible with Cruz in the race.

As reported by the Houston Chronicle, which confirmed Cruz's plans to announce Monday, the Texas Senator plans to "crush" it among Tea Party voters and then peel off some libertarian support. This is the same group that Paul will need if he's going to broaden his constituency. Cruz offers those voters an opportunity to vote for an anti-establishment fighter for limited government without having to swallow Paul's foreign policy views.

Last month, I noted that a poll showing increased hawkishness on national security issues was a bad sign for Paul. Jim Antle, in response, noted at Rare that Paul overcame criticisms of his foreign policy in 2010, when he won his primary in Kentucky. But in 2010, his opponent, Trey Grayson, was seen as the establishment choice in a Tea Party-fueled wave election year. So when Grayson attacked Paul on foreign policy, he didn't have much credibility among conservative primary voters.

If Paul were merely trying to fend off attacks from like likes of Jeb Bush, then yes, perhaps Paul would have an opening. But with Cruz no doubt prepared to aggressively attack Paul for his foreign policy views, that narrow opening is likely closed.