Mr Trump has told reporters he likes "Taylor's music about 25% less now".

The singer-songwriter, 28, had previously deliberately steered clear of politics but said events in "the past two years" had changed her mind.

Her latest comments were praised by many but also sparked a fierce backlash from Republican supporters.

Swift broke her silence on politics on Sunday, publicly endorsing two Democrats in Tennessee, her home state, in a post on Instagram, where she has 112m followers.

"In the past I've been reluctant to publicly voice my political opinions, but due to several events in my life and in the world in the past two years, I feel very differently about that now," she wrote.

A Buzzfeed News report quotes Vote.org's Kamari Guthrie, who says the site has seen a "registrations spike specifically since [her] post" in Tennessee, and also a bump in voter registration nationwide.

Swift particularly criticised Republican Senate nominee Marsha Blackburn for her voting record on gender equality.

"Her voting record in Congress appals and terrifies me," she wrote, citing the politician's votes against equal pay and domestic violence legislation.

Speaking on Monday, Mr Trump said Ms Blackburn was "doing a very good job" in Swift's home state.

"She's a tremendous woman," he said. "I'm sure Taylor Swift doesn't know anything about her."

In previous tweets posted in 2012, the US President had described Swift as "fantastic" and "terrific", and had thanked her for taking a picture with him.

Swift's post has been "liked" more than 1.6m times since she shared it on Sunday, including by model Chrissy Teigen, singer Katy Perry and actress Reese Witherspoon.

However, she has attracted criticism from conservative commentators and Republicans.

"What I used to love about Taylor Swift is she stayed away from politics," Charlie Kirk, founder of the conservative student organisation Turning Point, told Fox News on Monday.

Meanwhile, the National Republican Senatorial Committee criticised her "attitude", and said Swift had "[come] down from her ivory tower to tell hardworking Tennesseans" how to vote.

Swift did not publicly back any candidate in the 2016 election when other stars like Beyonce and Lady Gaga hit the campaign trail on behalf of Hillary Clinton.

In 2012, Swift told Time magazine she didn't talk about politics "because it might influence other people".

"I don't think that I know enough yet in life to be telling people who to vote for," she said at the time.

Swift has previously been criticised for avoiding discussion about politics - and a top Google search around the time of the 2016 elections was "Who is Taylor Swift voting for?"

Observers have argued that her political neutrality helped her popularity with country music fans.

Meanwhile, many online have pointed out that Swift wading into politics in support of the Democrats puts her again at odds with US rapper Kanye West - a vocal supporter of President Trump and frequent wearer of a Make America Great Again hat.

West and Swift have been in an on-off public feud since the rapper famously interrupted an acceptance speech she made at the 2009 MTV Music Video Awards.

Tennessee, a Republican-leaning state, is set to vote on 6 November in an election that could frustrate the US president's legislative agenda for the rest of his two-year term if his party loses its majorities in Congress.