WASHINGTON D.C. (CNN) -- Call it a mad dash for campaign cash.
GOP presidential hopeful Mitt Romney speaks at a "Rally for Romney" fundraiser on Friday in Salt Lake City, Utah.
White House hopefuls are out on the trail this weekend, cramming in as many fundraising events as possible. So what's the rush?
Sunday not only brings to a close the month of September, but it also is the last day the presidential campaigns can raise funds that will be counted in the third quarter of this year.
Come Monday, the campaigns have to report how much money they've raised the past three months. And other than national and state polls, campaign cash is one of the best numerical barometers to measure a candidate's strength.
Clinton will show she has pulled in between $17 to $20 million while Obama will report he raised between $18 and $19 million, sources close to each candidate told CNN.
Fundraising is historically slow in the third quarter, which covers the final two months of summer and the first month of fall.
In the second quarter, Obama shattered fundraising records by reporting that he raised $32.5 million, $31 million of which he can use in his bid for the Democratic nomination.
Clinton raised $27 million during this same period and all but $6 million of it can be used in the primary.
The numbers could change since the fundraising deadline isn't until midnight Sunday.
Sources at John Edwards' campaign told CNN they expect to report around $7 million in the third quarter. The former senator from North Carolina raised just over $9 million in the second quarter.
Edwards told CNN on Thursday that he will accept public financing for his run for the White House, subjecting himself to strict spending limits. Nine months ago, Edwards told CNN that he would follow Clinton's lead and not pursue the public financing option.
So what happened? Edwards said he was not trying to sound "holier than thou," and acknowledged he at one time intended to skip public financing.
"I myself thought early in this campaign about the possibility of not taking public financing," he said. Edwards added that when he sees "Washington money, the way it is, and when I am on the campaign trail, I constantly hear from people outside of Washington how worried they are about the way the system is functioning."
New Mexico Gov. Bill Richardson raised nearly $7 million last quarter and more than $13 million for the year. Analysts will be keeping a close eye on whether he can keep up his pace.
On the Republican side, expect former New York Mayor Rudy Giuliani and former Massachusetts Gov. Mitt Romney to battle again for the top spot. Romney raised nearly $35 million so far this year, with Giuliani $1.5 million behind.
Sources close to the Giuliani campaign say they expect to be atop of the pack for the third quarter.
Fred Thompson's numbers will be closely scrutinized. The former senator from Tennessee formally jumped into the race for the White House earlier this month after testing the waters since late spring. A source inside the campaign said that Thompson will report raising more than $7 million in the third quarter.
Sen. John McCain of Arizona is expected to show he raised more than $5 million this quarter but a McCain adviser told CNN that the McCain's recent poll numbers in New Hampshire and a busy fundraising schedule next month show that they "have some life." McCain raised $24.5 million the first two quarters of the year but spent nearly all of the funds raised.
Expect lower numbers for Sen. Sam Brownback of Kansas, Rep. Duncan Hunter of California, Rep. Ron Paul of Texas, Sen. Tom Tancredo of Colorado and former Arkansas Gov. Mike Huckabee. E-mail to a friend
All About U.S. Presidential Election