Bernie Sanders Won't Fully Commit to Closing Controversial Gun Control Loophole As the race tightens, Clinton and Sanders have ramped up their attacks.

CHARLESTON, South Carolina -- Shortly before visiting Emanuel AME Church in downtown Charleston where nine people were killed last summer in a mass shooting, Vermont Sen. Bernie Sanders would not fully commit his support to closing the so-called “Charleston loophole,” a gun control provision which allowed the accused shooter to purchase his gun.

"We are going to take a look at that as well," the presidential hopeful told ABC News' George Stephanopoulos Sunday on "This Week." "But what is most important is that we have a strong instant background check. I have supported that from day one. At the end of the day, what almost every American understands is we have got to keep guns out of the hands of people who should not have them. That has been my position since as far back and I can remember."

During the services at the church, the Jewish senator from Vermont bowed his head and prayed as a pastor intoned that "we know that no place is safe."

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The timing is especially significant to Sanders, as he battles back accusations from Hillary Clinton's campaign that he's soft on gun control. This weekend he announced his support for a bill that will roll back liability protection for gun manufacturers, though he has hesitated to support other measures like closing the so-called "Charleston loophole."

The topic is sure to arise at the Democratic debate tonight, the final chance for candidates to square off before the Iowa caucuses.

Last month in an email to supporters, Sanders said he was in favor of overturning the provision in the law that allows the sale of a gun to move forward if the federal government fails to return a background check in three days, as happened in the Charleston shooting.

"Congress should act to ensure the standard for ALL gun purchases is a completed background check. No check -- no sale," the email said.

The alleged gunman, Dylann Roof, was able to purchase his gun after five days despite having a felony drug charge on his record, the FBI said last year. After he tried buying the gun, the background check missed that Roof had admitted to possessing drugs during a previous arrest, which should have barred him from completing the purchase.

As the race for the Democratic nomination tightens, Clinton and Sanders have ramped up their attacks and rhetoric against each other. Speaking earlier on "This Week," Clinton accused Sanders of flip-flopping on another gun control issue.

The Vermont senator released a statement Saturday evening, on the eve of the next Democratic debate, saying he supported a new bill being circulated in Congress that would repeal the liability protections for gun manufacturers.

"I think the bill makes a lot of sense," said Sanders, who voted for the original law. "What we will do is be supportive of this legislation."

He added, “There is an amendment though that I want to see incorporated into it ... which monitors the impact on gun shops in rural America."

ABC News Brad Mielke contributed to this report.