Rep. Mark Kirk (Ill.) is leading several GOP Senate contenders by a wide margin while state Treasurer Alexi Giannoulias works to put away a field of Democrats, according to a new Chicago Tribune poll.

Kirk, whose centrist positions on certain issues have led to some speculation about his primary vulnerability, is not over 50 percent. But no other candidate appears to have asserted him- or herself as a strong alternative with a month and a half to go in the primary.

Kirk has 41 percent, compared to 3 percent for developer Patrick Hughes. Several other candidates are in the 1-3 percent range.

Giannoulias leads former Chicago Urban League President Cheryle Robinson Jackson 31-17 on the Democratic side, with former Chicago Inspector General David Hoffman at 9 percent and attorney Jacob Meister at 1 percent.

As the only female and African-American candidate in the race, Jackson leads Giannoulias 45-13 among black voters. But Giannoulias, the favorite in the race, maintains a two-to-one lead among women.

Much as with the Republican primary, Giannoulias appears to be benefiting from the lack of a single alternative, with Hoffman and Jackson splitting the vote against him. Jackson has also been at a significant financial disadvantage.