Hillary Clinton has kept the battle for the Democratic Party presidential nomination wide open with victories in the key states of Ohio and Texas.
On the Republican side, John McCain clinched the nomination by winning Tuesday's four primaries. Here is a round-up of US media reaction to the results.
JAY COST, REALCLEARPOLITICS.COM
After the Wisconsin primary there was evidence of pro-Obama momentum.
There is no evidence of this from yesterday's two big contests in Ohio and Texas.
In fact, Clinton not only regained ground she lost with her best groups, she made marked improvements among key portions of Obama's best groups.
One constant we saw again in Ohio last night was that Clinton did well among late deciders.
For months before his victory in Iowa, doubters questioned whether Obama had the stomach to deliver the blows necessary to wear down Clinton's advantages. Now, the question is whether he can take a punch...
Some Obama supporters are increasing pressure on him to shift tactics, frame more sharply his criticism of his opponents and begin inoculating himself from the GOP [Republican] attacks, but Obama remains reluctant to change the approaches that he still thinks will secure him the nomination.
LOS ANGELES TIMES
In winning New Hampshire a few weeks ago, Hillary Rodham Clinton declared, 'I found my own voice'.
But it was a much different voice in the closing days before Tuesday's voting that carried her to victory in Ohio and Texas - and which now lets her make a strong case for extending the Democratic presidential race into the spring and possibly beyond.
Gone was the misty-eyed Clinton who scored points showing her human side.
Gone was the gracious Clinton who, just two weeks ago, drew thunderous applause for expressing her pride in running against Barack Obama.
The new voice was angrier, sharper and far more negative toward Obama - a voice that at one point bellowed at her rival, "Shame on you," as she pushed back against what she said was an unfair attack.
WALL STREET JOURNAL
After her victory yesterday in Ohio and a nail biter in Texas, we see little reason that the New York senator shouldn't fight on.
That wouldn't please the Democratic panjandrums who desperately want a nominee now that John McCain has wrapped up the Republican race.
The party super delegates who were all for Mrs Clinton when she was "inevitable" are now hoping she'll drop out and spare them a painful decision.
A herd of them - they prefer the camouflage of numbers - have reportedly even been plotting to break together for the Illinois orator.
For Democrats, having the race go on is a mixed blessing.
Party elders have to worry that while McCain can now consolidate his support and organise for the fall, Obama and Clinton are still at each other's throats.
On the other hand, more competition is a boon for Democratic voters, who are getting an unexpectedly long look at the contenders.
The fight mobilises Democratic voters. It also fascinates the press and forces McCain to struggle for attention.
Little of the conventional wisdom about this race has panned out. McCain wasn't supposed to win, and Clinton was an inevitable winner. The race would be over by Super Tuesday. Obama's string of February victories made him unstoppable. Voters keep surprising the pundits. And that's exactly the way it should be.
JONATHAN MARTIN, POLITICO.COM
Despite the elation of the moment, McCain and the GOP face a difficult task.
Retaining the White House for three consecutive terms is no easy feat.
And with an unpopular Republican incumbent, deep concerns about an uncertain war, a shaky economy and a better-funded and more-energised Democratic Party, it will be that much more challenging for the Republicans to win this fall.