When Jackson Browne sued John McCain in 2008 for using his hit song Running on Empty in a campaign video, he was making a stand for musicians and songwriters who have long complained that politicians shouldn't be allowed to use their copyrighted material without direct permission.

That Browne, a longtime liberal activist with a particular interest in environmental issues, called out McCain, the conservative Arizona senator who had backed the Iraq invasion, was also part of the story. Citing federal trademark law, Browne argued that McCain's use of his song falsely implied an endorsement from the singer/songerwriter.

Ultimately, Browne's case was strengthened by the fact that Running on Empty was used in a McCain campaign video produced by the Ohio Republican Party. The unauthorized reproduction of the song crossed a thick legal line. McCain's lawyers were told by a judge that if Browne's case were to go to court, he'd probably lose.

In July 2009, the Arizona senator agreed to an out-of-court settlement.

Flash forward to last week in Cleveland when Donald Trump strode triumphantly onto the stage at the Republican National Convention to the music of Queen's glorious anthem We Are the Champions. Immediately afterward, Queen's remaining band members tweeted that they objected to the Republican Party's use of the song, written by Freddie Mercury, who was gay and died in 1991 at age 45.

As with McCain, Trump hadn't directly paid Queen or asked the band for permission to use Champions at the convention. But then again, he didn't have to.

Political campaigns often play songs at rallies after paying a performance rights organization such as the American Society of Composers, Authors and Publishers a fee to publicly air any song in their library. ASCAP represents more than 10 million musical works from more than 575,000 composers, songwriters, lyricists and music publishers.

A collective license from ASCAP requires a relatively small payment each time a song is played and precludes a campaign or venue such as Cleveland's Quicken Loans Arena from having to pay an individual musician or songwriter for the use of their song.

"If the RNC or Quicken Loans had a license, which they did, then technically they're covered under the public performance license," said Andrew Sparkler, an attorney at Downtown Music Publishing, which represents artists in technology and copyright issues. "As long as there's that license, that covers it."

Or does it? 

William Hochberg, a media lawyer at Los Angeles law firm Greenberg Glusker, counters that when it comes to a candidate's political rally, a song such as We Are The Champions is playing a greater role in that event than, say, background music at the Macy's Thanksgiving Day Parade down Manhattan's Fifth Avenue.

After all, this is politics, Hochberg said, and listeners could equate Trump's use of We Are the Champions or McCain's use of Running on Empty with a tacit endorsement or loose affiliation between artist and politician.

"They're going to say, 'We have the license, we didn't exceed the scope,'" Hochberg said. "But the artist can say: 'You put together a program that included our song. That's not ambient, that's a very important part of how you're trying to portray your candidate.'"

On that note, a group of artists -- Usher, Sheryl Crow, John Mellencamp and Heart's Wilson sisters -- put together a charmingly acerbic counterattack against politicians that use their songs without their personal approval. Sung to the tune of We Are the World, the video of Don't Use Our Songs became the focus of a typically searing segment on Last Week Tonight with John Oliver on Time Warner's (TWX) HBO.

The video's underlying message, Hochberg said, speaks to the unique qualities of music, and in the age of the Internet, the pervasive assumption that music isn't a piece of property in the same way as a car, a computer or even a film. Usher, Crow and company argue that the artist alone should be able to decide whether their works are associated with a political candidate.

"This is an abuse," Hochberg added. "Using music to get a lot of punch, and a lot of bang for no bucks, that's what's going on here."

Trump also has used the Rolling Stones' Sympathy for the Devil and R.E.M.'s It's the End of the World As We Know It (And I Feel Fine) at his rallies, proving he may have a very lively sense of humor. Both the Stones and R.E.M. have told him not to. (Heart made clear it didn't like Sarah Palin using their song Barracuda when she ran with McCain in 2008 on the Republican ticket.)

The backlash by musicians speaks to the blurriness of music rights. While copyright law allows for general use of a song, musicians have gone to court citing the Lanham Act, better known as the Trademark Act of 1946, which prevents false endorsement. But courts have differed in their application of Lanham, leaving no clear definition as to what constitutes unfair use.

Often candidates don't want the bad publicity of a musician objecting to their song use, as when Isaac Hayes put the kibosh on Bob Dole's use of Soul Man in 1996, or David Byrne doing the same to Florida's Charlie Crist in 2010 over his use of Road to Nowhere. In both cases, the candidates agreed to stop using the songs, and in Crist's case he made an undisclosed payment to Byrne.

Trump, in effect, is using the same lack of clarity in the law that YouTube owner Alphabet (GOOG - Get Report) asserts to dodge criticism that it isn't sufficiently paying artists to use their songs, especially when those songs are posted by third parties. 

The pushback by artists comes as musicians continue to pressure businesses such as YouTube for a greater share of the money they generate from their music. But in both cases, Downtown Music's Sparkler said, politicians and streaming platforms have come to view music as being free of charge.

"People think of music as different from physical property -- they think of it as ephemeral, as something they're entitled to," he said. "Unfortunately, there is a thread here, a loose ideological thread between a permissiveness to use these songs however anyone wants and a permissiveness by YouTube and others to pay whatever it wants to use the music. Right now, that's how things are."