With a new Des Moines Register/Bloomberg survey of Iowa Republicans showing Texas Sen. Ted Cruz taking a 10-point lead over Donald Trump in that state, Cruz’s rivals are sharpening their criticism of him.

Some of the harshest anti-Cruz rhetoric comes from Florida Sen. Marco Rubio.

Rubio said on NBC’s “Meet the Press” Sunday that Cruz “voted against the Defense Authorization Act every year it came up. … I assume if he voted against it he would veto it as president, that’s the bill that funds our troops and even the Iron Dome for Israel. So 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.”

He also charges that Cruz, by voting last June to end the National Security Agency’s bulk collection of telephone metadata, has undermined efforts to disrupt terrorist plots.

The two senators’ votes do reveal differences on surveillance, as well as on indefinite detention of terrorist suspects, U.S. overseas commitments, government shutdowns and immigration, but their roll call votes also show that they see eye-to-eye on many issues.

They have both voted to:

Disapprove President Barack Obama’s nuclear deal with Iran.

Reject Chuck Hagel as Defense secretary in 2013.

Approve building the Keystone XL pipeline.

Oppose a ban on workplace discrimination due to sexual orientation or gender identity.

Reject a 2013 bill that would have expanded the background check system for gun sales.

During the nearly three years they’ve spent together in the Senate, Cruz’s presidential support score on roll call votes where the Obama administration has taken a position is slightly lower than Rubio’s: 42.6 percent to 45.5 percent. Both are below the GOP Senate average during that time of 52.4 percent.

So how can a Republican primary voter tell them apart?

Cruz has been happy to make the extra effort to demonstrate an in-your-face opposition to Obama: He was one of only three “no” votes on John Kerry’s nomination to be secretary of State. Cruz cited Kerry’s “long record of supporting treaties and international tribunals that have undermined U.S. sovereignty.”

The three issues that bring the Cruz-Rubio differences into sharpest contrast are surveillance, U.S. commitments overseas and immigration.

Surveillance

In June, Cruz voted for and Rubio voted against the USA Freedom Act, which ended the NSA’s bulk collection and storage of telephone metadata as part of its effort to stop terrorist attacks.

The bill, Rubio said, “weakens U.S. national security by outlawing the very programs our intelligence community and the FBI have used to protect us time and time again.”

Cruz said the bill, which 23 Senate Republicans voted for, “ends the federal government’s bulk collection of personal data from law-abiding citizens,” but also “ensures that we maintain the tools that are needed to target violent terrorists and prevent acts of terror.”

On another intelligence-related set of votes, Cruz voted against confirmation of CIA Director John O. Brennan in 2013 and CIA General Counsel Caroline Krass in 2014. Rubio voted for both nominees.

Despite his vote for Brennan, Rubio joined Cruz in lending rhetorical support to Kentucky Sen. Rand Paul’s March 6, 2013, filibuster of the Brennan nomination to protest what Paul said was the Obama administration’s refusal to say whether drone strikes could be used on U.S. soil to kill Americans who’d been accused of terrorism, but who posed no imminent threat.

On another national security issue where Cruz and Rubio split, Cruz voted in June against the defense authorization bill (HR 1735) “because I made a promise when I was elected to office that I would not vote for an NDAA that continued to allow the president to violate the constitutional rights of American citizens by indefinitely detaining them without due process.” Rubio missed the June vote, but the pair split on the similar 2014 version.

Obama has said he wouldn’t authorize the indefinite military detention without trial of American citizens, even if such detention would be permissible under the 2001 authorization to use military force or under the 2012 defense authorization law.

But Cruz, Paul, and Utah Republican Sen. Mike Lee say that Congress ought to pass a law barring indefinite military detention without trial of U.S. citizens.

Overseas Interventions

Cruz is more skeptical than Rubio about long-term U.S. military engagements and foreign aid. Cruz, for example, voted against tabling Paul’s amendment to a 2013 spending bill that would have cut off U.S. aid to Egypt until that country conducted a democratic election. Rubio joined 32 other Republicans in voting to table the Paul amendment.

Rubio, much more in the interventionist and internationalist tradition of Arizona Republican Sen. John McCain and former President George W. Bush, has favored assertiveness in use of U.S. forces and aid to those trying to topple dictators.

During the Libyan uprising in 2011, he called for U.S. intervention to help rebels depose Moammar Gadhafi. Rubio assailed Obama for not acting quickly to impose a no-fly zone, saying in March 2011, “The United States, quite frankly, looks weak in this endeavor.”

In June 2011, as a member of the Foreign Relations Committee, Rubio voted for a resolution authorizing the use of military force in support of the NATO no-fly zone in Libya, but prohibiting the use of U.S. ground troops there.

But Cruz argued in a speech at the Heritage Foundation last week that “we do not have a side in the Syrian civil war” and that sometimes dictators such as Gadhafi in Libya and Bashar al-Assad in Syria may be preferable to the disorder sparked by their overthrow.

“We will not win by replacing dictators, as unpleasant as they may be, with terrorists who want to kill us and destroy America,” he said.

Cruz depicts Libya as an object lesson in the unintended consequences of U.S. interventionism. In October, he said tyrants such as Gadhafi were preferable to the disorder sparked by their overthrow.

“Some of the Republicans,” Cruz said, presumably referring to Rubio, “supported Hillary Clinton’s disastrous Libya policy. Toppling Gadhafi? Gadhafi was a bad guy but you know what? Libya is an absolute chaos and war zone where jihadists are battling back and forth.”

Immigration

Rubio was a member of the Senate’s informal, bipartisan “gang of eight” which in 2013 pushed for an immigration bill that would have allowed illegal immigrants to apply for legal status and eventually seek citizenship.

“If we don’t solve this issue, illegal immigrants are still going to be here illegally, people will continue to come in, people will continue to overstay their visas, and our broken legal immigration system will stay in place,” Rubio told CNN at the time.

He has since edged back from that bill, saying a comprehensive immigration measure isn’t a good idea and lacks political support.

But Rubio claims that Cruz’s position on immigration “is not much different than mine. He has supported in the past, and has said he is still open to supporting, legalizing people that are in this country illegally.”

A look at the record from the Judiciary Committee’s markup of the bill in 2013 casts some doubt on Rubio’s portrait of two men in basic agreement.

It’s true that during the markup Cruz, a member of the committee, said, “I don’t want immigration reform to fail. I want immigration reform to pass.”

But the substantive amendments Cruz offered, all of which were defeated in committee, would have made the bill much tougher on illegal immigrants and focused it more on increasing legal immigration, especially for skilled workers under the H-1B visa program. Almost all of the amendments Cruz proposed would have made the bill unacceptable to the gang of eight.

Most significantly, Cruz proposed removing a core feature of the gang of eight bill that would have made those illegally in the United States eventually eligible for U.S. citizenship.

“I believe for this legislation to solve the problem, there should not be a pathway to citizenship for those who are here illegally,” Cruz said during the markup. By insisting on a path to citizenship, he charged, the bill’s sponsors were “setting this bill up for defeat.”

In the end, the GOP-led House took no action on the Senate-passed bill, which Cruz voted against both in committee and on the floor.

Government Shutdowns

Cruz is perhaps best known for forcing a partial shutdown of the federal government in 2013 as a way of protesting Obama’s Affordable Care Act.

In October 2013, Rubio joined Cruz in voting against a continuing resolution that ended the shutdown.

But the following year — seven weeks before the 2014 elections when the Senate faced another vote on a continuing resolution and the potential of another shutdown — Rubio voted for the CR while Cruz was one of the 12 Republicans voting no.

Rubio did support Cruz on a procedural vote to try to allow other amendments to be offered, including one that Cruz wanted as a way of putting Democrats on the record in support of Obama’s executive actions halting deportation of some immigrants who had entered the United States illegally.

While many voters judge presidential contenders on debate performances or rhetorical virtuosity, roll call votes sometimes matter. Just ask Hillary Clinton about her 2002 vote to authorize the invasion of Iraq.

While there are no votes exactly comparable to that one in the Rubio-Cruz record, there are enough differences that could help Republican primary voters choose one conservative over another.

A version of this story originally appeared in the Dec. 7 issue of CQ Weekly.