With the Iowa caucuses less than two months away, presidential candidate Donald Trump continues to dominate the field of candidates in the Republican primary race, but because Ben Carson has plummeted to third or fourth place in most of the national polls, Sen. Ted Cruz and Sen. Marco Rubio have surged and could pose to challenge Trump’s top-dog status.

Cruz and Rubio continue exchanging barbs over who is the most hawkish on national security, but as Cruz appears to be the clear favorite among conservative Republicans, Evangelicals, and is pulling away from Marco Rubio in most of these national polls, Rubio has reverted to conducting a “crush Cruz” political campaign.

Rubio, for whatever reason, believes that tying Cruz to Rand Paul—saying that he is weak on national security for siding with “isolationists” when he voted in favor of a bill that would cut some data-mining provisions of the Patriot Act—will work to peel away voters in the early voting states. On NBC’s Meet the Press, Marco Rubio said:

He talks tough on some of these issues, for example he’s going to carpet bomb ISIS. But the only budget he’s ever voted for in his time in the Senate is a budget that cut defense spending by more than Barack Obama proposes we cut it.

Rubio added:

My point is each time he’s had to choose between strong national defense and some of the isolationist tendencies in American politics, he seems to side with the isolationists. This is an important issue to have a debate over. It’s not personal.

In this little “MMA match” between Cruz and Rubio, Cruz and others are effectively counter-punching Rubio by saying that, because he embraced the failed Obama agenda when he cosponsored and promoted the controversial Senate “Gang of Eight” comprehensive immigration reform bill in 2013, Rubio is really the weak one on national security.

Let’s go back to 2010, when Marco Rubio said this:

First of all, earned path to citizenship is basically code for amnesty. It’s what they call it. And the reality of it is this: This has to do with the bottom line that America cannot be the only country in the world that does not enforce its immigration laws.

It is unfair to the people that have legally entered this country to create an alternative pathway for individuals who entered illegally and knowingly did so. If you do that, you will never have a legal immigration system that works. No one is going to follow the law if there’s an easier way to do it [become a citizen].

While Marco Rubio’s case against Cruz can be perceived as anemic, at best, Cruz and Rand Paul’s attacks against him—where they tie immigration reform and national security together and paint Rubio as “weak” on national defense—may turn out to be more effective than Rubio’s dig against Cruz.

Expect serious fireworks over national security between Cruz and Rubio in the upcoming Las Vegas debate and in the coming weeks.