After more than a month with little or no traction, the Never Trump movement is approaching its last stand. Only 10 contests remain in the presidential primaries and it is in the next state of Indiana - which votes on Tuesday - where the movement is now focusing its energies.
At stake are 57 delegates, the second-largest delegate haul remaining, and experts say Texas Senator Ted Cruz must win the state.
"For Cruz, Indiana is not significant, it is crucial. If he cannot win here, the campaign has no momentum and no reason for continuing," said Dr John Karaagac, a political science lecturer at Indiana University Bloomington.
To achieve this win, Mr Cruz and Ohio governor John Kasich formed an alliance this week, which allowed for a two-way race between Mr Trump and Mr Cruz in Indiana, and between Mr Trump and Mr Kasich in Oregon and New Mexico.
Said Dr Karaagac: "They are doing what they should have done earlier, which is to force the contest with Trump into a binary choice, with the Trump challenger playing on favourable territory."
The Never Trump movement continues to pump money into attack advertisements in Indiana and beyond. According to the Centre for Public Integrity, groups have spent millions on about 60,000 TV ads critical of Mr Trump, and about 800 or so have aired in Indiana.
But the extent to which this will help Mr Cruz is debatable.
"If Cruz wins... it will have happened regardless of the supposed Cruz-Kasich agreement," said assistant professor of political science Aaron Dusso from Indiana University-Purdue University Indianapolis. "Kasich said that he still thinks people in Indiana should vote for him. So the alliance doesn't seem to actually be of much significance."
Mr Cruz has been campaigning hard in Indiana over the past few days, and tried to eclipse Mr Trump's major foreign policy speech on Wednesday by naming former Hewlett-Packard chief executive Carly Fiorina as his vice-presidential running mate - a very unconventional move at this stage of the primary contest.
Some experts believe it is Mr Cruz's last-ditch attempt to stay relevant, after Mr Trump swept all five East Coast primary states on Tuesday, leaving Mr Cruz with no mathematical path to winning 1,237 delegates and clinching the nomination on the first ballot.
According to political website Real Clear Politics, which takes an average of available polls, Mr Trump is ahead by only 6.3 percentage points, so it does seem like Mr Cruz still stands a chance.
"I'd say Indiana has more religious conservatives than many other states and those individuals have responded better to Cruz so far this primary season," said Dr Dusso.
The Midwest, which includes Wisconsin where Mr Cruz won decisively, also has a different political culture from the North-east and the South, where Mr Trump has dominated the field.
The political culture is "less bellicose", said Dr Karagaac, and would not be as favourable to Mr Trump's brash style.
With that in mind, the Never Trump movement continues to pump money into attack advertisements in Indiana and beyond.
According to the Centre for Public Integrity, groups have spent millions on about 60,000 TV ads critical of Mr Trump, and about 800 or so have aired in Indiana.
But it will still be an uphill task for Mr Cruz and the Never Trump movement to dispel the sense of inevitability surrounding the Trump campaign.
"Cruz has to craft a message for Indiana Republicans which is based on governing, sensibility as opposed to bravado, and a constitutional message," said Dr Karaagac. "In theory that can work; in reality the clock is working against Cruz."
Others are less optimistic about stopping Mr Trump at this late stage.
"I don't think the Never Trump movement will be able to change much, going forward. I would predict that Republicans will start to accept the inevitable and fall in line behind Trump," said Dr Dusso.
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