CHARLESTON, S.C. -- Democratic presidential candidate Bernie Sanders never asked Rep. James Clyburn, South Carolina's senior Democrat, to endorse him ahead of Saturday's Democratic primary, Clyburn said Tuesday.

Clyburn endorsed front-runner Hillary Clinton last week, though he had previously said he would remain neutral until after his state's first-in-the-South primary vote. Neither candidate had actively lobbied him in public, but Clinton had said she would welcome the endorsement when the time came.

Sanders "never asked me for an endorsement, and so I never considered giving one," Clyburn said of the senator from Vermont. "The debate I was having was between my head and my heart. My head was staying neutral, and my heart was always with Hillary."

Speaking to reporters in a telephone news conference arranged by the Clinton campaign, Clyburn said Tuesday that he has "nothing against" Sanders, has worked with him in Congress and had met with him or spoken to him several times since Sanders entered the race last spring.

But Clyburn said he was been unable to get the Sanders campaign to agree to shift its policy position on allocation of federal anti-poverty resources and to accommodate more black colleges in the signature Sanders proposal for free public college tuition. Clyburn said the Sanders college plan would "undercut and destroy" private, historically black colleges and universities.

The Sanders campaign denies that the free tuition program would threaten historically black institutions, about half of which are public and half private. Sanders toured several historically black schools last week and spoke at Morehouse College, which is private.

Clyburn also rejected criticism from Sanders allies that Clinton is "pandering" to African American voters ahead of the South Carolina vote. The primary will be the largest test to date of the candidates' strength among African American voters, who make up a majority of Democratic voters in the state. Clinton is polling far ahead of Sanders in South Carolina.

"I guess you always try to find where the sweet spot on anything might be," Clyburn said, but that does not mean that outreach to the crucial black vote equals pandering. And Clinton's résumé shows she has not come lately to issues of racial justice, Clyburn said, citing her work in the 1970s on behalf of juvenile offenders and children in the South.

"She wasn't running for president," at the time, Clyburn said. "Who was she pandering to back then?"

Clyburn is the third-ranking Democrat in the House, and the unofficial dean of South Carolina Democrats.

Clinton was campaigning in South Carolina later Tuesday alongside African American mothers who have lost children to police action or gun violence.