Hillary Clinton sharpens attacks on Donald Trump

At her final Kentucky event Monday night, Hillary Clinton treated supporters to some debate prep, anticipating Trump's lines on jobs, reports CBS News correspondent Nancy Cordes.

"If one answer is, 'I'm going to do it, I know how to do it, I'll get it done, but I'm not going to tell you what I'm going to do... " she said.

But Clinton still needs to get through Sanders first, and needs 144 delegates to clinch the nomination. She did not mention the man who is likely to beat her Tuesday in one, possible two states. Sanders spent the day in Puerto Rico, which doesn't vote for about three weeks - a signal he intends to go the distance.

"If elected president of the United States, you will have an ally in the Oval Office," he told the crowd.

His tenacity in the final stretch has forced Clinton to campaign in primary states that likely won't be competitive in the fall. Still, Democratic leaders won't pressure him to drop out, careful not to alienate his millions of supporters.

"Right now we have two great candidates," House Minority Leader Nancy Pelosi said. "Bernie Sanders is broadening the universe of people who are paying attention to the political process."

"Do you think he's hurting your likely nominee?" Cordes asked.

"No, I think Bernie Sanders and Hillary Clinton and the Democrats have a message focused on helping the middle class," said Sen. Chuck Schumer, D-New York.

To help Clinton, one of the biggest pro-Clinton super PACs has begun airing its first anti-Trump ads ahead of schedule to help Clinton. One features women lip synching some of Trump's most divisive lines about women.

It's no accident that this first ad focuses on women. According to CBS News exit polls, they made up 53 percent of the electorate in 2012 and polls show women hold overwhelmingly negative views about Trump.

If Democrats can cement those views, Clinton will have a much easier time in November.