That’s according to the POLITICO Caucus — a panel of activists, strategists and operatives in 11 key battleground states. More than seven-in-10 GOP insiders, 71 percent, say the polls understate Trump’s support because voters don’t want to admit to pollsters that they are backing the controversial Republican nominee.

With Trump falling behind in the majority of swing states, an overwhelming polling error may represent his best hope to win next month — and even that may not be enough. At the same time GOP insiders say there are “shy Trump” voters out there who aren’t showing up in the polls, a 59-percent majority still say Clinton would win their state if the election were held today.

“I’m not sure how big a factor it is, but there is definitely a ‘Bradley effect’ going on out there,” said a Virginia Republican, referring to the African-American mayor of Los Angeles who led in polls but lost unexpectedly in the 1982 California gubernatorial race. “I personally know many Republicans that won’t admit that they are voting for Trump. I don’t like admitting it myself. It won’t matter if Hillary is up more than 5 points, but we might be in for a surprise if Hillary’s lead is less than 5 points on Election Day.”