Watch CNN South Carolina Democratic Town Hall Highlights VIDEO

Hillary Clinton and Bernie Sanders confronted issues of race Tuesday at a CNN town hall four days ahead of the South Carolina Democratic primary in which African-American voters will play a crucial role.

Sanders accused Republican presidential front-runner Donald Trump and others of fomenting a “racist effort” to delegitimize President Barack Obama. Sanders portrayed the “birther” controversy that Trump pushed during Obama’s first term as part of a Republican strategy to thwart his presidency, based on the mantra “obstruct, obstruct, obstruct.”

“We have been dealing in the last seven years with an unprecedented level of obstructionism against President Obama,” Sanders said.