SEOUL -- Protesters were out in force again to stop any vehicle headed to the controversial U.S. anti-missile system called THAAD that was installed here in the middle of the night two weeks ago.

"We're blocking this road to make sure that this van isn't carrying supplies for THAAD," said one protester.

Villagers are against the U.S. system because they fear it will only increase the threat of war as North Korea continues to bully the region with its missile program.

Protests against the THAAD system, and the U.S., have now become a key part of the country's Tuesday presidential election.

Moon Jae CBS News

Liberal candidate Moon Jae, a human rights activist, has surged in the polls and says South Korea must learn how to say "no" to America. He opposes THAAD and also argues sanctions aren't enough to stop the North and talks with Kim Jung Un must continue.

Cheol-Soo Ahn CBS News

His main opponent, Cheol-Soo Ahn, is a doctor who made his fortune as a software mogul before entering politics. He, like President Trump, went to the Wharton Business School in Pennsylvania. Ahn says that would allow him to build a rapport with Mr. Trump.

He initially opposed THAAD, but now favors it -- a reversal most see as a bid to attract conservative voters.

A protester near the site of the THAAD missile system CBS News

The next 24 hours will show if he's right.

"THAAD is not problem of this village. It's problem of Korean Peninsula, it's problem of world peace," one of the protesters said.

No matter who wins, the U.S. may find itself on the back foot. Both leading candidates favor talking to North Korea over the U.S.-led effort to further isolate it.