10 PHOTOS Bernie Sanders through the years See Gallery 2016 candidate attracting crowds in thousands as others pull in hundreds Senator Bernie Sanders, an independent from Vermont and 2016 Democratic presidential candidate, speaks during an event in Iowa Falls, Iowa, U.S., on Monday, Jan. 25, 2016. With a week to go until the Iowa caucuses and the Democratic presidential race there in a virtual dead heat, Hillary Clinton and Sanders are mapping out divergent paths toward winning the first votes of the nomination process. Photographer: T.J. Kirkpatrick/Bloomberg via Getty Images Washington, UNITED STATES: Newly-elected senators meet with Senate Minority Leader Harry Reid (R), D-NV, in Washington, DC 13 November 2006. From left are: Senator-elect James Webb, D-VA, Senator-elect Bernie Sanders, I-VT, Senator-elect Amy Klobuchar, D-MN, and Reid. AFP PHOTO/Karen BLEIER (Photo credit should read KAREN BLEIER/AFP/Getty Images) US Congressman Elliot Engel (L) takes pictures next to US Senator Bernie Sanders after being dressed as Bouale leaders by public notaries of the Kouadioyaokro village, 150 km from Abidjan, 09 November 2008. US Senators Tom Harkin and Bernie Sanders visit comes ahead of a July 2008 certification deadline to ensure cocoa heading to the United States -- the third largest importer of Ivorian cocoa -- has not been produced with child labour. AFP PHOTO/ISSOUF SANOGO (Photo credit should read ISSOUF SANOGO/AFP/Getty Images) COLUMBIA, SC - APRIL 25: Potential Democratic presidential candidate Sen. Bernie Sanders (R) (I-VT) delivers remarks at the South Carolina Democratic Party state convention April 25, 2015 in Columbia, South Carolina. Sanders joined former Maryland Gov. Martin O'Malley and former Sen. Lincoln Chafee in speaking to the convention. (Photo by Win McNamee/Getty Images) WASHINGTON, DC - APRIL 20: U.S. Sen. Bernie Sanders (I-VT) participates in a 'Don't Trade Our Future' march organized by the group Campaign for America's Future April 20, 2015 in Washington, DC. The event was part of the Populism 2015 Conference which is conducting their conference with the theme 'Building a Movement for People and the Planet.' (Photo by Win McNamee/Getty Images) U.S. Senator Bernie Sanders, an Independent from Vermont and 2016 U.S. presidential candidate, greets supporters during a campaign rally in Madison, Wisconsin, U.S., on Wednesday, July 1, 2015. Sanders said he had attracted 200,000 donors as of mid-June and his campaign had raised $8.3 million online through June 17, according to FEC filings by ActBlue, the fundraising platform that he and some other left-leaning candidates and causes use. Photographer: Christopher Dilts/Bloomberg via Getty Images PORTLAND, ME - JULY 6: Vermont Sen. Bernie Sanders speaks at the Cross Insurance Arena while campaigning in the Democratic presidential primary. (Photo by Derek Davis/Portland Press Herald via Getty Images) Supporters hold up signs at a campaign rally for Senator Bernie Sanders, an Independent from Vermont and 2016 U.S. presidential candidate, in Madison, Wisconsin, U.S., on Wednesday, July 1, 2015. Sanders said he had attracted 200,000 donors as of mid-June and his campaign had raised $8.3 million online through June 17, according to FEC filings by ActBlue, the fundraising platform that he and some other left-leaning candidates and causes use. Photographer: Christopher Dilts/Bloomberg via Getty Images PORTLAND, ME - JULY 6: Vermont Sen. Bernie Sanders speaks at the Cross Insurance Arena while campaigning in the Democratic presidential primary. Sen. Bernie Sanders greets supporters after speaking in Portland. (Photo by Derek Davis/Portland Press Herald via Getty Images) PHOENIX, AZ - JULY 18: U.S. Sen. Bernie Sanders (I-VT) speaks to the crowd at the Phoenix Convention Center July 18, 2015 in Phoenix, Arizona. The Democratic presidential candidate spoke on his central issues of income inequality, job creation, controlling climate change, quality affordable education and getting big money out of politics, to more than 11,000 people attending. (Photo by Charlie Leight/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

PORTLAND, Maine (AP) — Democratic presidential candidate Bernie Sanders can sure pack 'em in. He recently drew a crowd of 10,000 in Madison, Wisconsin, and another 7,500 this week in Portland, Maine.

But for Sanders to turn his insurgent campaign into a viable challenge against unquestioned front-runner Hillary Rodham Clinton, he will need to covert those willing to come hear him speak in the summer of 2015 into volunteers, donors and voters in 2016.





And for all the crowds that Sanders is attracting, he remains far behind Clinton in the work of building a campaign organization.

Right now, Sanders has a little more than 50 paid staffers in all. Clinton has nearly 50 in Iowa alone, as well as at least one in all 50 states.