The Latest: House Speaker Paul Ryan refuses to back Trump

WASHINGTON - The Latest on campaign 2016 (all times Eastern):

4:15 p.m.

House Speaker Paul Ryan is refusing to support Donald Trump as the Republican nominee for president.

Ryan is the GOP's highest-ranking office holder and made the stunning announcement on CNN's "The Lead" on Thursday.

It comes two days after Trump essentially clinched the nomination with a commanding win in Indiana that forced his last two opponents from the race.

Ryan says he wants to be able to support Trump but that he's not there yet. He says Trump has work to do to unify the party.

Ryan says many Republicans want to see "a standard-bearer who bears our standards" and "unifies all the wings of the Republicans Party."

3:20 p.m.

Hillary Clinton is urging Democrats to unite around her candidacy, telling an audience of black community leaders in Los Angeles that her lead among pledged delegates and votes against Bernie Sanders is much wider than Barack Obama's edge over her in 2008.

Clinton says at the California African American Museum that she is more than 3 million votes ahead of Sanders and nearly 300 pledged delegates ahead of him. She says when she was running against Obama in 2008, they were "neck and neck" in the popular vote and he had a lead of about 60 pledged delegates.

Clinton says she "knew that he had won because it matters how many delegates you have, whether it's 60 or 300."

She says "we've got to work hard and win big here in California in the primary to get ready for the general election" and she will do "everything I can to unify the party."

2:20 p.m.

Hillary Clinton's presidential campaign is starting a new "Stop Trump Fund" to raise money off businessman Donald Trump's emergence as the presumptive Republican nominee.

Clinton's campaign manager Robby Mook says in an email to supporters that the fundraising drive will "make sure that Trump can never use the power of the presidency" to deport millions of immigrants, prevent Muslims from entering the United States or "punish" women who get abortions.

The campaign is sending free stickers to people who donate to the fund, which will raise money for Clinton's primary campaign against Democratic rival Bernie Sanders.

2 p.m.

With their champion, Sen. Ted Cruz, now out of the presidential race, groups opposing abortion and same-sex marriage say they'll bide their time and warily assess Donald Trump before deciding whether to back him as the Republican nominee.

During months of campaigning, Trump has made some statements about abortion and gay rights that pleased social conservatives and others that unsettled them. That inconsistency, coupled with various liberal-leaning comments he made in past years, has deprived Trump of an enthusiastic embrace by the social conservative camp.

Now, with Trump the presumptive GOP nominee, there are recalculations being made by activist leaders who had backed Cruz, such as Tony Perkins, president of the conservative Family Research Council. Perkins says key factors will include who Trump picks as his running mate.

12:35 p.m.

Don't expect to see Mitt Romney at the Republican Party's national convention this summer.

An aide to the GOP's 2012 presidential nominee confirms that Romney isn't planning to attend the convention where Donald Trump is expected to become the Republican Party's 2016 presidential nominee. The aide spoke on the condition of anonymity to share internal discussions.

Romney has been an aggressive critic of Trump. The former Massachusetts governor vowed earlier in the year that he'd rather write someone in than vote for Trump in the general election.

Trump became the GOP's presumptive nominee this week after both of his remaining rivals dropped out of the race.

12:25 p.m.

Freshman Republican Sen. Ben Sasse says America should draft an alternative to Donald Trump and Hillary Clinton, someone who would be an "honest leader" and "an adult."

"Why are we confined to these two terrible options?" Sasse writes in a manifesto titled "An Open Letter to Majority America."

"This is America. If both choices stink, we reject them and go bigger. That's what we do," he says.

Sasse, who has been an outspoken critic of Trump, doesn't offer a preferred candidate - although over Twitter he's mentioned former Oklahoma Sen. Tom Coburn.

But he says after discussions with his constituents it's clear that voters want a better option. Nebraska's Republicans have yet to vote in the presidential election; their primary is May 10.

11:30 a.m.

Donald Trump says he has nothing against Janet Yellen but would likely replace her as Fed chair once her term is up.

In an interview with CNBC, the likely Republican presidential nominee says he thinks it would be appropriate for him to nominate someone else to lead the Fed since Yellen is not a Republican. President Barack Obama selected Yellen to succeed Republican Ben Bernanke. Her four-year term as Fed leader ends on Feb. 3, 2018.

Trump says he has "absolutely nothing against" Yellen, calling her a "very capable person." While Yellen's term as chair ends in 2018, she could remain as a governor on the Fed's seven-member board. Her 14-year term as a Fed board member does not end until Jan. 31, 2024.

11:25 a.m.

Donald Trump is tapping private investor Steven Mnuchin to lead his presidential fundraising.

Trump is a celebrity businessman who largely financed his primary bid through personal loans to his campaign. He says that while he will continue to put up "substantial money," he must also develop a more traditional fundraising approach now that he is likely to face off with Democrat Hillary Clinton in the general election.

Mnuchin is chairman and chief executive officer of Dune Capital management LLC, a private investment firm, and previously worked at the New York bank Goldman Sachs.

Trump says in a statement that he has worked with Mnuchin "in a business capacity. Mnuchin "brings his expertise in finance to what will be an extremely successful fundraising operation for the Republican Party," Trump says.