Although Ted Cruz has insisted he will not personally attack Donald Trump as the race for the Republican nomination heats up, supporters of the Texas senator appear to be weighing how best to target Trump in Iowa, where Cruz holds a narrow lead.

A message-testing phone call in Iowa on Monday floated seven distinct lines of attack against the national frontrunner, asking whether each one would make the listener more or less likely to support him.

Kedron Bardwell, a political science professor at Simpson College in Iowa, received the call and recorded detailed notes, which he provided to RealClearPolitics.

One potential attack noted Trump’s recent remark “to a Christian audience in Iowa that he has ‘never asked God for forgiveness.’” Another depicted Trump as “a New York liberal pretending to have conservative values.”

Two potential attacks targeted the billionaire businessman’s loyalty to the GOP — one noting that he had changed his party ID, the other mentioning his Reform Party candidacy for president in 1999/2000 and his prior financial support for Democrats.

Three other attacks cited Trump’s stances on eminent domain, abortion and single-payer health care, respectively.

Although calls of this nature cannot be definitively traced to a campaign or outside group, the content typically hints at the sponsor. In this case, following the series of potential attacks on Trump, the call posed an open-ended question about Cruz’s support in Iowa, asking whether any message recently has made Cruz more or less favorable to the respondent.

Polls to test potential campaign messages, like this one, are not uncommon. But floating attacks on Trump could signal a shift in strategy to come among Cruz’s supporters in Iowa.

The message-testing call comes as the race to win Iowa has apparently narrowed to Cruz and Trump, both of whom lead Marco Rubio, the third-place Republican, by double digits in the RealClearPolitics polling average.

Cruz’s allies do appear to be keeping Rubio on their radar: Along with the potential attacks on Trump, the call sought reaction to four current ads featuring Rubio, in addition to Trump’s first television ad and three ads featuring Cruz (one negative and two positive).

Belying Cruz’s public nonchalance about his chief rival, the call also sought to gauge the damage done in Iowa by Trump’s suggestion that Cruz’s birth in Canada could make him ineligible for the presidency, although Cruz’s mother was American.

The call asked whether the respondent had heard about Trump’s accusations that Cruz is not a natural-born citizen, and whether they believe Cruz is eligible to run for president. The call also asked the listener whether Trump’s charge against Cruz would affect their vote.

Cruz has publicly dismissed Trump’s suggestion as nonsense, characterizing it in a CNN interview as one of many “fevered swamp theories” on the Internet. But Trump continued to describe the issue as a “problem” for his opponent during a rally Monday in New Hampshire.

This article was updated at 12:13 p.m. Jan. 12.