Campaign finance

Democratic presidential candidate former Vice President Joe Biden wishes Barbara Moroney, of Rocky Point, N.Y., a happy 80th birthday on the phone during a campaign rally, Tuesday, Feb. 4, 2020, in Nashua, N.H. (AP Photo/Mary Altaffer)

Democratic presidential candidate former Vice President Joe Biden clenches his fist as he speaks at a campaign event, Wednesday, Feb. 5, 2020, in Somersworth, N.H. (AP Photo/Elise Amendola)

People wait for results at a caucus night campaign rally for democratic presidential candidate former Vice President Joe Biden on Monday, Feb. 3, 2020, in Des Moines, Iowa. (AP Photo/John Locher)

FILE - In this Sept. 19, 2019 file photo, Democratic presidential candidate former Maryland Rep. John Delaney speaks at the Climate Forum at Georgetown University in Washington. Delaney, the longest-running Democratic candidate in the 2020 presidential race, is ending his campaign after pouring millions of his own money into an effort that failed to resonate with voters. (AP Photo/Jose Luis Magana)

Democratic presidential candidate and former New York City Mayor Michael Bloomberg, center, greets supporters at a campaign office, Monday, Jan. 27, 2020, in Scarborough, Maine. (AP Photo/Robert F. Bukaty)

This undated image released by the House Judiciary Committee from documents provided by Lev Parnas to the committee in the impeachment probe against President Donald Trump, shows a photo of Lev Parnas with Rudy Giuliani. Parnas, a close associate of Trump's personal lawyer Giuliani is claiming Trump was directly involved in the effort to pressure Ukraine to investigate Democratic rival Joe Biden. Trump on Thursday, Jan. 16, 2020, repeated denials that he is acquainted with Parnas, despite numerous photos that have emerged of the two men together.(House Judiciary Committee via AP)

FILE - In this Jan. 9, 2020, file photo, President Donald Trump points as he arrives to speak at a campaign rally, in Toledo, Ohio. As the Democratic primary intensifies ahead of the first voting contests, President Donald Trump and his allies have issued a series of favorable comments about Democrat Bernie Sanders. It's a strategy aimed at trying to take advantage of Democratic divisions and trying to attract some Sanders' supporters to Trump's campaign if the senator is not his party's nominee. (AP Photo/ Jacquelyn Martin, File)

This undated image released by the House Judiciary Committee from documents provided by Lev Parnas to the committee in the impeachment probe against President Donald Trump, shows a photo of Lev Parnas with Trump in Florida. Parnas, a close associate of Trump's personal lawyer Rudy Giuliani is claiming Trump was directly involved in the effort to pressure Ukraine to investigate Democratic rival Joe Biden. Trump on Thursday, Jan. 16, 2020, repeated denials that he is acquainted with Parnas, despite numerous photos that have emerged of the two men together. (House Judiciary Committee via AP)

FILE - In this Jan. 19, 2020, file photo, Democratic presidential candidate Michael Bloomberg speaks at the Greenwood Cultural Center in Tulsa, Okla. They are circling each other like wary boxers, with taunts on Twitter, snarky asides and belittling depictions of one another. They rose to prominence in Manhattan on parallel tracks, amassed wealth real and perceived and displayed a penchant for putting their names on things. President Donald Trump and Mike Bloomberg could hardly be more different as people but now they both want the same job: Trump’s. (AP Photo/Sue Ogrocki, File)

Democratic presidential candidate Sen. Bernie Sanders, I-Vt., speaks at a campaign stop at the State Historical Museum of Iowa, Monday, Jan. 20, 2020, in Des Moines, Iowa. (AP Photo/Andrew Harnik)