Hillary Clinton's devastating losses in Maryland and Virginia this week came about as a result of an erosion in what had been her solid edge among women, white people and older and working-class voters.
While the results can be explained by those states' relatively large numbers of Black people and well-educated residents - who tend to be Barack Obama supporters - her presidential campaign could be doomed if the trends continue.
Commentators have estimated that Obama is now the frontrunner to become the Democratic Party's candidate for American president with more than 50 votes lead over Clinton and the winning of seven states in a row.
But his rival is holding onto some of her supporters who are largely defined by race and often by level of education, such as low-income white workers and older white women, exit polls of voters show. She's been losing other blocs, again stamped by personal characteristics, such as Black people, men and young people both Black and white, and better-educated white people.
The latest defeats have slowed the one-time favorite's political momentum at a bad time. With Obama winning eight straight contests and easily outdistancing her in money raising, she must now endure three weeks until primaries in Texas and Ohio that she hopes will resurrect her campaign.
Clinton's losses have also enabled Obama to take a slight lead in their crucial fight for convention delegates. With 2,025 needed to clinch the nomination at the party's Denver gathering in August, Obama has 1,275 delegates to Clinton's 1,220, according to the latest count by The Associated Press.
Before this year's presidential contests began, Obama was running consistently behind his rival in the polls. The Illinois senator was mostly attracting upper-echelon white people, young people and about half of Black voters - resembling the coalitions that sealed defeat for past non-establishment Democratic candidates such as Gary Hart and Bill Bradley.
Things have changed since the voting has started, especially after bitter exchanges during the Clinton-Obama contest in South Carolina highlighted their racial differences and, subsequently, former Senator John Edwards exited the race.
Now, virtually all Black people support Obama, significant since they make up about a fifth of Democratic voters overall.
And while last year's polls showed Clinton leading among men, Obama now leads her among males by 11 percentage points, according to exit polls of voters in 20 competitive Democratic primaries.
Before Tuesday's voting, the two were even among white males this year. Obama defeated her among that group by 18 percentage points in Virginia - his first win with white men in a Southern state - and they divided white men about equally in Maryland. Obama has done especially well with men who are college educated.
Tuesday's voting highlighted the ground Clinton has lost with groups that have been strongholds of her support.
In both Virginia and Maryland, she got the backing of only about four in 10 women and three in 10 men. Obama narrowly edged her among white people in Virginia, while she won among Maryland white people by 10 points.
In each state, she got 45 per cent of voters 65 and over, and just over one-third of people earning under $50,000 annually or with high school degrees or less.
At the same time, Obama won huge margins among Black people, young voters, higher-income and better-educated people, leaving Clinton nowhere to turn for support.
She had the misfortune of Democratic primaries in two states in which about one-third of voters were Black and about two-thirds of voting white people were college-educated, exit polls showed. Both are unusually high numbers, an all-but inevitable recipe for Obama triumphs.
A closer look shows more about the voters Clinton was losing and keeping, and underscores the importance of race and education in the contest.
While Clinton lost among people making less than $50,000 annually, she got six in 10 votes from whites in both states making that amount. The same was true for people over age 65 and those with no more than high school degrees - she lost both groups overall, but was backed by about six in 10 white people in those categories.
Nationally, 54 per cent of college-educated white men voting in Democratic primaries have supported Obama, compared with 33 per cent of those without college degrees. Maryland's figures on Tuesday were virtually identical to that, while in Virginia 62 per cent of college-educated white men backed Obama, compared with 48 per cent who are not graduates.
The figures from Tuesday's voting came from an exit poll conducted by Edison Media Research and Mitofsky International in 30 precincts each in Maryland and Virginia for the Associated Press and television networks.
Those interviewed included 1,245 Democrats in Virginia and 1,324 in Maryland, with a margin of sampling error for each of plus or minus four percentage points. Also, 719 Virginia Republicans and 690 in Maryland were interviewed, with sampling error margins of five points for Virginia and 6 points for Maryland. Margins of sampling error for subgroups were larger.
National figures come from earlier exit polls conducted by the two companies.