If Donald Trump becomes the Republican Party’s presidential nominee, many voters may stay home in November. At least that’s what prominent Republican strategist Karl Rove is predicting.

Rove, who was a top adviser to President George W. Bush, made his comments late Wednesday at an event held by technology company SAP at the Newseum in Washington, D.C., the Hill reported. He spoke with Democratic operative David Plouffe, who worked on President Barack Obama’s campaigns, and the two answered questions about a potential matchup between Trump and Hillary Clinton.

General election turnout had been increasing for several years, but 2012 saw a significant drop off in registered voters who came out to cast their ballots for either Mitt Romney or Obama. So far, Republicans have seen high turnout rates during their primary season, and Trump has been quick to claim credit for this. He has appealed to many independents and first-time voters, but it is unclear if the primary turnout increases are due to people voting for him or against.

Trump’s campaign has also largely moved through the primary season without developing extensive ground operations. Rove warned this could be a vulnerability in the general election, according to the Hill. While discussing data use, he said that if Trump does not “change his understanding of the voter he’s talking to” beyond primaries, he could suffer in the general.

As for general election turnout, Rove expressed skepticism that the phenomenon of Trump would bring more people to the polls.

“We’re going to have a much larger group of people, and I don’t know what [amount] it is, who look at both of these candidates and see two flawed people and say, ‘I’m trying to decide between two not-great choices,’"he said, referring to Trump and Clinton. “And therefore, they’re going to find it more difficult to make a decision and stay with a decision.”

Rove, who helped run Bush’s presidential campaigns, is a frequent critic of Trump and has often taken to Twitter to attack or mock the Republican front-runner. He also wrote an op-ed for the Wall Street Journal earlier this year that said Trump could cause the GOP to lose the White House, the Senate and many of its House spots.

While Trump holds a wide lead over his competitors at 673 delegates, he still has to win a majority of the remaining delegates in order to reach 1,237 — the number needed to clinch the nomination. His next closest competitor is Texas Sen. Ted Cruz, who has 410 delegates, followed by Ohio Gov. John Kasich, who has 143.