Two of the most prominent outside groups funding efforts to prevent Donald Trump from winning the Republican nomination will spend heavily in Wisconsin, the next primary state, NBC News has learned.
Our Principles PAC is making a "very robust" investment in the state to fund a cable television ad buy, digital ads, direct and phone calls targeting Republican primary voters. The television ads are expected to be on air Monday.
The decision by Our Principles PAC was announced Friday, one day after another anti-Trump group, the Club for Growth, announced its own $1 million advertisement buy in the Badger State. Together the two groups have spent about $15 million on anti-Trump messaging in the Republican primary.
With only 17 Republican primary contests remaining, Wisconsin, the next state to vote, is a critical opportunity for Donald Trump opponents to hinder his candidacy.
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The decision to continue to spend money in the primary is based, in part, on the success Texas Sen. Ted Cruz had in the latest contests, particularly in Utah, where he won the support of more than 50 percent of caucus-goers, showing his candidacy still has some strength left. In addition, poll numbers show that Cruz is in striking distance of Trump in Wisconsin.
Those two factors have led a cohort of 30 to 40 conservatives who convened in Washington last week to plot ways to stop Trump at the convention or through a third party to be optimistic about Cruz's chances to prevent Trump from winning the nomination. Therefore, they will wait to see what happens in Wisconsin before determining their next move.
Conservative radio host Erick Erickson, organizer of the meeting, said there's "a real strong feeling now" that Cruz could stop Trump from winning a majority of the delegates.
If Cruz does not perform well in Wisconsin, Erickson said that discussions about a third party option could be revived quickly. The Constitution Party holds is convention less than two weeks later. The Libertarian Party is also considered an outlet for disillusioned Republicans.
While it's going to be extremely difficult to win the remaining 85 percent of delegates he needs to win the nomination, Cruz can prohibit Trump from reachingthe magic number of 1237. Wisconsin awards 42 delegates, a portion of them given to the statewide winner and others given to the winner of each Congressional district.
With a majority of states having already voted, each opportunity becomes more important for the anti-Trump movement. After Wisconsin, which is April 5, the next state to vote isn't until New York on April 19.
In the Club for Growth ad, the narrator encourages voters to support Texas Sen. Ted Cruz over Ohio Gov. John Kasich as necessary to prevent Trump from winning the state.
"If you don't want Donald Trump to win, your choice comes down to this: Math." the narrator says. "To stop Trump, vote for Cruz."
The Kasich team, however, is not happy with the ad. The chief strategist for the super PAC backing Kasich, New Day for America, called the Club for Growth a "special interest group run by a bunch of Washington, DC hacks and has-beens."
This article originally appeared on NBCNews.com.