Republican nominee Donald Trump speaks at "Joni's Roast and Ride" in Des Moines, Iowa, US, August 27, 2016. [Photo/Agencies]

WASHINGTON - US Republican presidential nominee Donald Trump could feel some pain from a new line of political ads from his Democratic rival Hillary Clinton's team depicting him as a racist, at a time when he is trying to catch up in the polls.

Clinton's campaign this week put out a new TV advertisement claiming that among Trump's supporters are the Ku Klux Klan (KKK) -- a white supremacist group that has killed, terrorized and intimidated blacks and other minorities in the United States, although the group has very little power now compared to when it was in its heyday several decades ago.

While Trump has no ties to white supremacists, the ad makes the case that they support him and that if he wins they will run the country.

Experts said the ads could hurt Trump and damage his campaign, which is just three months from the November elections.

"They are damaging for Trump because they draw on things he or his campaign have done to paint a picture of someone who is completely insensitive to the concerns of the minority community," Darrell West, vice-president and director of governance studies of the Brookings Institution, told Xinhua.

The ads not only reinforce points already made that Trump is rude and impolite, but also take this critique several steps further by labeling him a racist, West said.

For his part, Trump blasted the ads as untrue, while using social media to refute Clinton's attacks.

But that move is risky for him, as experts say Trump must get the public eye off of his bombast and onto Clinton's perceived missteps and corruption while she was secretary of state.

Experts also argued that the New York businessman should continue his message that law and order is declining in the United States, and that a Clinton presidency would only exacerbate this, as Clinton would be an extension of the current Obama administration.

Trump has a few times tried to do this by making cogent and well-argued speeches on US foreign policy and the economy, only to later ruin any gains he might have made by reverting back to insults and bombast.

In the past week Trump has resisted the temptation to make over-the-top statements that hurt him with the broader American electorate, but it remains unknown how long he can do this.

"The risk for him is that he gets off his law and order message and has to defend himself from the racism charge. It never helps a candidate to have to give an 'I'm not a racist' defense," West said.

Dan Mahaffee, an analyst with the Center for the Study of the Presidency and Congress, told Xinhua that Trump did avoid the temptation to go off script and has been more effective in message discipline recently.

If Trump continues to focus on hitting back on Clinton and avoiding collateral damage, he may turn the corner and start to close some of the polling gap that has him behind Clinton in key states, Mahaffee said.

US media has exposed that Clinton has in the past closely associated with known racists, as shown in her statements in 2010 when she referred to former Senator Robert Byrd, a KKK member, as a mentor and friend.