Sen. Marco Rubio holds a town hall meeting in Nashua, N.H., on Thursday. (Charles Ommanney/The Washington Post)

A super PAC ad hitting Sen. Ted Cruz last month for supporting a “Canadian” style value-added tax plan piled on the insults, saying Ronald Reagan “hated” the idea and noting that the Wall Street Journal warned it could lead to higher taxes.

The spot by Conservative Solutions PAC, a super PAC allied with Sen. Marco Rubio of Florida, was posted online about a week after Rubio campaign staffers tweeted a link to a rapid-response site that made the exact same points.

The close correlation of messages shows how easy it is for well-funded independent groups to decipher the needs of the candidates they are supporting. While campaigns are prohibited under federal law from coordinating their advertising strategy with super PACs and other outside groups, the narrowly written rules leave ample room for them to share information online.

Open telegraphing is becoming increasingly common. Candidates routinely post raw video footage that can be used in ads by outside allies, such as the hours of b-roll interviews with Cruz’s family uploaded last summer to his Senate YouTube page. Former Hewlett Packard chief executive Carly Fiorina posts her schedule to a public calendar, which her allied super PAC follows to determine where to send advance staff.

“The law still prohibits campaigns and super PACs from talking directly to each other, but the regulations haven’t kept up with modern communication technology,” said GOP election law attorney Benjamin Ginsberg, who served as counsel for the presidential campaigns of George W. Bush and Mitt Romney.

“That means campaigns and super PACs are communicating publicly in plain view, in compliance with the wording of the existing regulation,” he added.

Jeffrey Sadosky, a spokesman for Conservative Solutions PAC, declined to comment on whether the group is using research from a Rubio campaign web site called 2016Facts.org.

“We make our decisions based on a number of factors, including polling and the actions of all the candidates and their PACs,” he said. “There is no one factor that drives our decision-making.”

When asked if tweets by campaign officials were effort to signal the super PAC, Rubio spokesman Alex Conant replied, “We follow the law.”

With little action coming out of a sharply divided Federal Election Commission, the 2016 election has already seen markedly bold examples of campaigns working in concert with outside groups financed by large donations. The Democratic super PAC Correct the Record is actually coordinating directly with Hillary Clinton’s presidential campaign, leaning on an FEC exemption originally designed for bloggers.

“That helped open up the flood gates,” Ginsberg said.

The Rubio campaign has been posting opposition research and talking points to 2016Facts.org. The site’s home page consists solely of a photo of Mount Rushmore and a folksy video of the senator answering top Google queries related to his name. Visitors are asked to sign up with their email to “learn the facts about the 2016 Election!”

The site is identified as paid for by the Rubio campaign, but it does not provide any visible links to its contents.

Conant said 2016Facts.org serves as the campaign’s fact-checking site and that the research posted there is widely disseminated through press releases, Twitter and Facebook.

“We have taken more negative attacks and false attacks and been the subject of more false reporting, including by the Washington Post, than any other campaign,” he said. “This site is where we set the facts straight for our supporters and credible reporters.”

He declined to comment on why there were no publicly visible links to the contents of 2016Facts.org, saying, “We don’t discuss our digital strategy.”

The contents of the website can be seen through links that have been tweeted by Rubio campaign officials.

“Get the facts on @JebBush and @r2rusa false TV ad,” Rubio senior adviser Joe Pounder tweeted at 11 a.m. on Dec. 29, referring to a spot released that day by the pro-Bush super PAC Right to Rise that slammed Rubio for missing national security briefings.

The Right to Rise ad had already caught the attention of strategists at Conservative Solutions PAC, who hours earlier had begun working on a response, according to a person familiar with the super PAC’s discussions.

In his tweet, Pounder provided a link to a page on 2016Facts.org pushing back against the Right to Rise ad.

Among the items highlighted on the page was an interview that Sen. Chuck Grassley of Iowa gave to a local TV station, in which he dismissed the idea that Rubio’s absence from Senate Foreign Relations Committee meetings was a big deal.

A few days later, Conservative Solutions PAC rolled out an ad in Iowa defending Rubio’s attendance record that declared, “Jeb Bush is desperate.”

“His attacks on Marco Rubio have been dismissed and debunked by our own Sen. Grassley,” says a male narrator in the spot, citing the same local Iowa TV interview with Grassley.

The super PAC’s anti-Cruz ad in January opened with a photo of the senator from Texas in a Canadian maple leaf-shaped frame. “Cruz wants a value-added tax, like they have in Canada and European socialist countries,” the narrator says.

The ad was uploaded a week after Rubio staffers tweeted a link to a 2016Facts.org research page headlined “Senator Ted Cruz supports a large new European-style tax called a Value-Added Tax.”

Under an FEC regulation adopted in 2010, campaigns cannot share private strategy with their outside allies, but independent groups can draw from “a publicly available source” to produce ads supporting a candidate.

“If communications are public, it’s not coordination,” said Kenneth Gross, a former FEC associate general counsel. “It gets down to the intricacies of the communication on social media, and generally people view Twitter as a public communication.”