There has been a change in the Republican presidential race over the past few days.
It may have been barely noticeable. But it is important and could have a significant impact come the general election in November.
Let's take things back to Friday. Donald Trump organised a big campaign rally in Chicago. Many people lined up before dawn to attend, but a significant number were not Trump supporters.
They were there to protest against the Republican frontrunner.
They weren't quiet or discreet while in the hall. They made their presence known and their voices heard.
At some point in the afternoon, the Trump campaign discussed things with the Chicago police. Donald Trump says they couldn't guarantee they had enough officers to cope with any unrest. The police say that simply isn't true.
Whoever is right or wrong, the Trump campaign decided to postpone the event.
As people left the hall, there were angry confrontations between Trump supporters and those who celebrated "shutting him down". With tensions high and emotions inflamed, a few of the exchanges erupted into fistfights.
The police cleared the hall, but that pushed the violence on to the streets where, again, there were a number of fights.
One American TV channel described the situation as a "near riot", but more measured heads said that while it was loud and angry, the clashes were small in scale and sporadic in nature.
Trump insisted that he did the right thing to protect people, saying "professional protesters" and "thugs" were inciting the crowd.
READ MORE: Donald Trump and electing Islamophobia
A short time after the cancellation, one of Trump's Republican rivals, Ted Cruz, spoke to the media. The Texas senator condemned those who would try to restrict the first amendment rights of others, but insisted that Trump himself had set the tone.
"When you have a campaign that disrespects the voters, when you have a campaign that affirmatively encourages violence, when you have campaign that is facing allegations of physical violence against members of the press, you create an environment that only encourages this sort of nasty discourse," Cruz said.
On the campaign trail Trump has had to face a lot of protesters.
At various times he suggested punching those who object in the face, throwing them out in sub-zero temperatures after removing their coat, and said that in times past such people would have left the hall "on a stretcher".
At a rally in North Carolina, a 78-year-old man hammered a forearm smash into the face of a demonstrator who was being led from the hall.
He has now been charged with assault and Trump says he's considering paying his legal fees.
But despite the problems in Chicago, Trump has not changed his approach
So what has changed?
READ MORE: Donald Trump blames Bernie Sanders fans for violence
On Thursday, during the last Republican debate, the candidates were asked if they would support the nominee no matter who it was.
But 48 hours later those positions appeared more flexible.
Florida Senator Marco Rubio told the media he didn't know if he could support Trump if he won. "It's getting harder each day," he said.
"You wonder if we're headed in a different direction today where we're no longer capable of having difference of opinion but in fact protests become a licence to take up violence and take on your opponents physically.
"American politics is turning into the comments section of a blog."
And Ohio Governor John Kasich, who has tried to keep his campaign positive, said if Trump won it would be "extremely difficult to support" the Republican ticket in November.
In a later interview he wouldn't say if he thought the billionaire businessman was fit to be president
For two senior Republican figures - candidates for the US presidency, no less - to question if they could support their own party in a general election is significant and indicative of how uncomfortable the party is with the rise of Trump.
It could actually split the Grand Old Party.
Trump's campaign has no precedent in modern presidential races. And it may actually change the face of politics in the US.
Source: Al Jazeera