The GOP anti-Trump forces are not yet done in terms of their efforts to bring the rampaging Trump truck to a halt. But, they are running out of time and the numbers are still not on their side.

The next great contest is set in Wisconsin and the Republicans who opposed Trump are launching a campaign for their last-ditch attempt to deny Trump of his presidential nomination aspiration.

The GOP's Moneyed Donors Are Ganging Up Against Trump

The final stages of attacks against the GOP frontrunner are getting a backing from some of the more affluent contributors from the conservative side. They are all hoping for the same outcome and that is to deny Trump from ever reaching the right number of delegates to secure the outright nomination. They are going all-out just for the brokered or contested convention to take place in July.

Take, for instance, Our Principles PAC -- the political action group received $4.8 million in donations from different donors for the month of February alone.

"You have all these people who backed different candidates, and now they are uniting," said political adviser Brian Baker. "These are people who backed Senator Cruz, Governor Kasich, Governor Christie, Senator Rubio -- all stripes. And they are all conservatives."

The Wisconsin Gameplan to Stop Trump

Another political group, the Club for Growth, has already outlined their course of action that would somehow slow down Trump's momentum and deny him of the needed 1,237 delegates. They sent out memos to their Republican donors, who pledged as much as $2 million for Wisconsin, regarding their strategy, like improving the chances of Ted Cruz to take away some delegates from Trump.

Cruz's team, meanwhile, is adding more staff in Wisconsin and setting up camp for their volunteers.

Trump is Stepping up his Campaign Efforts, Too

It seems like Trump just won't let himself get outdone by his rivals. For one, the real estate tycoon has shored up his own campaign in the last month with a $6.9 million spending in February from his very own cash coffers. That would bump up his total personal investment in the presidential race to a total of $25 million.

While the large chunk of his campaign money is self-funded, outside help has also poured in with a $9.5-million contribution from his supporters, which includes the $2 million cash inflow in February, according to the data by the Federal Election Commission.