won on Tuesday by a wide margin the Republican primary in Illinois.
Romney, a multimillionaire who has the backing of most influential Republicans, but has difficulty winning the support of right-wing party, has a wide lead over his main rivalin delegates to elect the candidate who will face President Barack Obama in the November elections.
A defeat in Illinois would have caused further doubt on Romney's ability to rally the party base.
Santorum, a Catholic supported by the religious right, almost no chance of reaching Romney on delegates.
The first exit poll survey in Illinois showed that Romney was the favorite of those seeking a candidate capable of beating Obama, and for those who fear for the state of the economy and the fiscal deficit.
Santorum has the support of those seeking a real right-wing candidate and a man of strong moral character, and those who base their choice on the religious aspect, but these are rare in Illinois voters.
Romney, former governor of Massachusetts, had 522 delegates before the Illinois primary, according to Associated Press count. Santorum was 252, 136 and Newt Gingrich50.
Delegates are allocated by elections or caucuses in each state and a candidate needs 1,144 delegates to at least make the nomination.
Neither Gingrich nor Paul made a lot of campaigning in Illinois. But Romney's inability to get rid of a rival apparently weak Santorum, a former senator from Pennsylvania who until recent months had few followers in the country, highlights the difficulties of his candidacy, which has aroused the enthusiasm of Republican electorate. It also forces you to invest time and enormous resources in the primaries instead of concentrating on defeating Obama.
In Illinois, Romney had an advantage in the competition for delegates to the Republican National Convention in August thanks to the greater organization.
Santorum could not aspire to 10 of the 54 delegates at stake because his campaign did not submit the required documentation.