As Rick Santorum tries to gain ground on Mitt Romney in the race for Republican delegates, Santorum’s late start in states other than Iowa continues to make it hard for him to compete for every potential delegate.

Santorum will not compete for delegates in four of Illinois’ 18 congressional districts, meaning he is only eligible to win 44 of the state’s 54 delegates at stake tonight.

But it could have been even worse.

Copies of Santorum delegate petitions provided to NBC News by the Illinois State Board of Elections also show that in 10 other districts, Santorum did not have enough signatures to qualify for the ballot. (In Illinois, a GOP candidate needs three people -- in most districts -- willing to be a delegate, plus 600 signatures to get on the ballot.)

The only way, however, for a candidate to be deemed ineligible is for a campaign to contest the signatures. In other words, the state is not going to check them unless a campaign officially asks it to do so.

The Romney campaign initially did challenge Santorum’s petitions in January, but dropped it after the Santorum campaign agreed to drop similar contests of Romney delegates, according to Jon Zahm, Santorum’s Illinois state director.

Santorum's campaign said it challenged the Romney delegates, because the petitions were notarized in Massachusetts, according to Zahm. (It's unclear, however, if that's the case or if notarizing out of state would have made the petitions invalid.)

While candidates run in a non-binding statewide primary in Illinois, the delegates run individually in congressional districts with their pledged presidential candidate printed next to their name. According to Illinois election law, each delegate must submit a petition to the State Board of Elections with at least 600 signatures in order to run.

The copies of Santorum’s petitions reveal he had fewer than 600 signatures in districts one, two, three, 10, 11, 12, 15, 16, 17, and 18. In seven of those districts, the petitions had fewer than half the required signatures.

Illinois is not the first state where a missed filing deadline has caused Santorum to lose out on delegates. On Super Tuesday, the Santorum campaign failed to meet filing deadlines in Ohio and Virginia causing the former Pennsylvania senator to forego competing for at least 55 delegates. Early next month, Santorum also failed to get on the ballot in the District of Columbia, where he will forego another 16 delegates in the district’s April 3 primary.

The delegate problems come in the context of a campaign where Santorum already faces a large delegate deficit. Based on delegates allotted by NBC News, Mitt Romney has 444 delegates, more than twice Santorum’s count of 183. (The state of Wyoming today switched one more delegate from Santorum to Romney.)

Santorum would have to significantly outperform his results so far in order to catch Romney and even approach getting the 1,144 delegates needed to secure the nomination.

Ballot difficulties

It is not easy to meet ballot access requirements in many states, and Illinois is only the latest example the Santorum campaign has seen of getting a late start in launching a national campaign. 

The Santorum campaign did not start its Illinois effort in earnest until late December, according to Zahm, and had only a couple of weeks to get on the state’s primary ballot. In fact, given the late start and lack of a large paid staff in Illinois, it is a testament to Santorum’s volunteers in the state that he is on the ballot at all.

“We started Dec. 23rd,” says Zahm. “We had a two-week campaign to get on the ballot.”

From there, the Santorum campaign faced significant difficulty. With candidates’ delegates running as individuals in each congressional district, the Santorum campaign faced an uphill battle gathering enough signatures for their slates of delegates in such a short amount of time.

In other words, it’s not enough getting the candidate on the statewide ballot; the campaign had to work hard to identify people who would run as delegates and then get hundreds of Illinois Republicans to sign their petitions.

Santorum did not even submit delegate slates, any signatures at all, in the fourth, fifth, and seventh congressional districts -- and a human error resulted in the campaign failing to get on the ballot in the state’s 13th district as well.

As campaign volunteers rushed to get all of the petitions submitted to the State Board of Elections by the 5:00 pm CT deadline on Friday, Jan. 5, volunteers left one of the petition envelopes unopened, and it was mistakenly thrown away. By the time the campaign tried to rectify the mistake with the elections office, the deadline had already passed and Santorum delegates could not get on the ballot.

Contested delegates

Suspecting the Santorum campaign did not have enough signatures, the Romney campaign challenged the petitions of Santorum delegates in the 10 congressional districts where copies of the petitions show Santorum did not, in fact, have enough signatures.

In response, Zahm counter-challenged and filed contests against the Romney delegates, arguing the Romney delegate petitions were notarized by a notary in Massachusetts, which made the petitions invalid. Ultimately, both sides dropped their contests.

“I let the Romney people know I was going after them on that,” Zahm said. “They eventually came to me and asked me to withdraw that complaint as long as they withdrew theirs.”

Romney state chairman Dan Rutherford, also Illinois treasurer, was not available to comment, but Romney spokeswoman Andrea Saul simply said the campaign decided not to force Santorum’s delegates off the ballot.

“Senator Santorum outright failed to qualify to be on the ballot in four congressional districts in Illinois,” said Saul in an email to NBC News. “However, in other districts where he fell short, it would have been incumbent on us or another campaign to force him off the ballot.  We decided against doing that.”

Saul blamed Santorum’s ballot problems on his own campaign.

“All of Sen. Santorum’s ballot-access problems have been a result of his own organizational failures,” Saul continued.

Santorum’s path ahead
The Santorum campaign acknowledges it will be difficult for any campaign to get to 1,144 delegates with four candidates in the race but remains confident they can still make inroads in the delegate race. In a conference call with reporters Tuesday, Santorum adviser John Yob, brought on by the campaign as a delegate strategist, said there is a path for the former Pennsylvania senator to get to 1,144.

According to Yob, the campaign rests its delegate strategy on over-performing in May contests like Arkansas, Kentucky, and Texas and then picking up delegates in states like Iowa and Minnesota, which held caucuses earlier, but do not actually bind delegates until county and state conventions in April and May.

As for the organizational deficiencies, Santorum himself said the campaign struggled with the arcane rules of states with early deadlines, but that the organization now is in good shape.

“It’s amazing that we’re on the ballots we are – given how difficult these rules are from state to state and how different they are and the fact that we used volunteers to get this done in December,” Santorum contended on MSNBC’s Morning Joe Monday. “Since that time, of course, we’ve been fine. We’re getting on the ballots and, of course, as you’ve seen, our organization is pretty darn good.”

As for tonight’s primary in Illinois, Zahm thinks Santorum can still make a good showing despite starting at an initial delegate disadvantage.

“There’s 14 districts we’re competing in,” Zahm said. “My campaign plan calls for winning 10 of them. If we win 10, we’ll win 10 out of 18 and we’ll have a majority.”