Hillary Clinton has firmed as favourite for the Democrats after a win in the Democratic primary in South Carolina.
And there are growing fears among the Republican establishment that billionaire Donald Trump could seal that party's nomination with a strong Super Tuesday showing.
If the campaigns for the nominations to run for United States president in November had not already seemed brutal, there is no question now.
But it is not so much the two major parties going head-to-head in the bitter verbal battles -- it is more like Republican versus Republican.
The party now faces the very real prospect of outsider Donald Trump securing its nomination for the presidency.
And sensing that, rival candidate and Florida senator Marco Rubio is not holding anything back in his assessment of the billionaire businessman.
"I really believed that voters would see through this con job that he's trying to do, and, obviously, that hasn't happened. He's convinced a lot of people, and now's the time where we have to address it. I believe a first-rate con artist is on the verge of taking over the party of (Abraham) Lincoln and (Ronald) Reagan, and, now or never, we need to remind people of what's at stake here. We're about to lose the conservative movement to someone who's not a conservative and (lose) the party of Lincoln and Reagan to a con artist."
Donald Trump has been characteristically forthright in his rebuttal.
"I call him Little Marco. That's what he is, he's Little Marco. But, you know, he's a very nasty guy. We're going to beat out the establishment. The establishment is disgraceful. Little Marco is doing not so well in Florida. He's down about 20 points, and the people in Florida can't stand him. He couldn't be elected dog catcher in Florida."
Marco Rubio and Texas senator Ted Cruz appear to be the only Republican candidates capable of slowing what has become the Trump juggernaut.
And Senator Cruz knows just how much is riding on Super Tuesday, when 11 states will vote on the party's nomination.
The election of almost 600 delegates to the party convention that will ultimately endorse the candidate is at stake, and he is calling out any anti-Trump vote.
"There is no doubt that, if Donald steamrolls through Super Tuesday, wins everywhere with big margins, that he may well be unstoppable. I don't think that'll happen. But I think, if you're at home and you don't want Donald Trump to be the Republican nominee, then the only candidate who can beat Donald is our campaign. And so I would encourage, even if you like another candidate, stand with us if you don't want Donald to be the nominee."
It is just as much a Super Tuesday for the Democrats as well, with 875 conference delegates up for grabs across 11 states.
Another four states will vote on the weekend.
Frontrunner Hillary Clinton goes into the big day buoyed by her convincing victory in South Carolina, as she told voters there.
"I am so greatly appreciative, because, today, you sent a message: In America, when we stand together, (cheering ...) when we stand together, there is no barrier too big to break. We have to stand with each other! We have to hold each other up, lift each other up, move together into the future that we will make! Thank you, God bless you, and God bless America."
Her rival, Vermont senator Bernie Sanders, has not tried to put much of a gloss on his defeat in the South Carolina ballot.
"Well, we got decimated, that's what happened. Among older African-Americans, it was pathetic, from our perspective. But by the way, what was ... the glimmer of positive news for us is that we won the 29-years-of-age-or-younger vote, and we did well with African-American young people as well as white young people. But, no question, Secretary Clinton won that state, and she won it big. But I'm in Minnesota now. I think we got a real shot at Minnesota. I think we got a shot at Colorado, Oklahoma, Massachusetts and Vermont. So we're looking to the future, not looking back."
But if the veteran senator cannot win over more African-American voters, the race could shape up by the end of the week as a Hillary Clinton-Donald Trump battle for president.
