We pieced together the family tree from a number of sources: a tombstone database, online genealogy sites, old newspapers. Giving us this family tree, with the Obama branch at left and the Wolf branch at right. It's explained below.
The common ancestors are Thomas McCurry and Margaret Belle Wright. (We know about their lives and children thanks to this overview of Obama's history.) But we get a little more detail from a 2009 interview with Wolf's mother, Anna McCurry Wolf. Her father's family, she said, "migrated into Kentucky, and Illinois is where my grandfather lived; Alten, Illinois." That's Thomas. "And he, at age three, shook President Lincoln's hand ... he was on my grandfather's shoulders, and this is Thomas Creekmore McCurry, and Lincoln just came over and shook his hand way up there. And I thought well, isn't that strange?"
Leona McMurry and her husband Rolla Payne had three kids, including Madelyn Payne, Obama's grandmother. Frank and Mabel had the aforementioned Anna McCurry. Anna McCurry married Curtis Wolf, who was also a physician. They had Milton.
Madelyn Payne married Stanley Dunham, and they had a daughter, Stanley Ann Dunham. She married a man from Kenya named Barack Hussein Obama. You know the rest of the story.
Perhaps the most charming part of the interview with Anna McCurry is her obvious excitement about being related to the president. She'd heard that the family was related to a black man from Chicago, and then saw his 2004 convention speech. When she heard him refer to a white grandmother from Kansas at some point, she told her second husband, Gene Colle, "that kid has to have the same DNA I have. That has to be Stanley Ann's son." It was. She traveled to D.C. with a group from Kansas, and met Obama, who gave her an autographed copy of his book. Then, the group ran into him in the Capitol.
Before he noticed me he shook everybody's hand in our group, and he said, “I understand you're all from Kansas,” and gave them all greetings. Then he gave me a hug and he said to them, “Now, you guys take care of my cousin.” So that was a really special time for me.
If her son has his way, he'll soon be walking the halls of the Capitol himself — but probably not with as generous an assessment of his distant relative.
Update: A confusing sentence about Anna McCurry's parents has been clarified, and Milton Wolf's birth year has been corrected.