Pop star Taylor Swift's decision to wade into electoral politics for the first time has driven a spike in online voter registration, particularly among young people, according to the website Vote.org.
Swift, who has largely eschewed politics even as she has become one of pop music's global superstars, told her followers she could not support Republican Marsha Blackburn due to the congresswoman's record on women's issues and gay rights.
View this post on InstagramA post shared by Taylor Swift (@taylorswift) on
Politics can be dicey for artists such as Swift with roots - and fans - in country music, the dominant genre of red state America.
In the post she also endorsed two Democratic candidates in her home state of Tennessee and urged people to register.
Swift's Instagram post had recommended people visit the website Vote.org.
The nonprofit site, which helps people register online, reported more than 250,000 new registrations since Swift posted the message.
By comparison, the site recorded 57,000 new registrations in all of August and 190,000 last month. More than 60 percent of the registrations since the post were among voters between 18 and 29 years old, an increase the site said was likely prompted by Swift's post.
"This is a pretty incredible, off-the-charts event," said Raven Brooks, the chief operating officer for Vote.org.
Vote.org acknowledged it was not possible to measure the direct impact of Swift's move, but Mr Brooks noted the surge in young voters was in line with Swift's youthful fan base.
Swift's enormous reach - she has 112 million Instagram followers and 84 million Twitter followers - underscores the way celebrities can leverage their online presence by sending messages instantaneously to millions of fans.
Grammy winner Rihanna in an Instagram post today also urged fans to register to vote - the last day in 14 states for citizens to register.
It was not the first time Rihanna has waded into US politics, although the singer is from Barbados and ineligible to vote because she is not an American citizen.
Polls show the US Senate contest between Democrat Phil Bredesen and Mrs Blackburn, a staunch supporter of President Donald Trump, virtually tied in a state Trump won by 16 points in 2016.
Mr Trump dismissed Swift as an uninformed voter.
"Let's just say I like Taylor's music about 25 percent less now, OK?," he told reporters.
Former Arkansas Governor Mike Huckabee also chimed in saying her endorsements "won't impact the election unless we allow 13 yr old girls to vote."
Many celebrities identify as liberals, and Democrat Hillary Clinton enjoyed broad support from actors, musicians and other popular figures in 2016.
The most notable celebrity to support Mr Trump may be the rapper Kanye West, who is set to have lunch with the president at the White House.
West and Swift engaged in a years-long feud after West interrupted Swift's acceptance speech at the 2009 MTV Video Music Awards.
- Reuters