U.S. Republican presidential candidate Ted Cruz speaks at a 2nd Amendment Coalition announcement at CrossRoads Shooting Sports in Johnston, Iowa, December 4, 2015. REUTERS/Brian C. Frank

Sen. Ted Cruz (R-Tex.) told volunteers Thursday he believes the Republican presidential contest will be decided in the next 90 days, but warned them to get ready for a nasty ride.

"I want to tell everyone to get ready, strap on the full armor of God, get ready for the attacks that are coming," a hoarse-sounding Cruz told volunteers on a conference call. "Come the month of January we ain’t seen nothing yet."

The call, part thank you and update to volunteers and part fundraising pitch where listeners could press a button to give a donation, comes after Cruz's campaign announced it raised nearly $20 million last quarter as the Texas Republican ascended in the polls in both Iowa, the nation's first voting state, and nationally.

Read: Cruz campaign raises more than $19 million in last quarter

Cruz said he believes the Republican nominee could be chosen by the end of March, despite the fact that the Republican primary calendar stretches until June.

"There is a very good possibility that the Republican primary will be decided by the end of March," he said, telling supporters starting Friday they are in a "90-day sprint to win this nomination."

Cruz sought to galvanize his current volunteer base, which the campaign said consists of 175,000 people nationwide, and recruit new members. The campaign is doubling the amount of space it has to house volunteers in Iowa and is opening a similar facility in New Hampshire. The campaign has sought to build a nationwide grass-roots coalition to support Cruz, and said it has 1,400 people on leadership teams in 19 states. It said it has county chairmen in all 171 counties in the nation's first four voting states.

The Texas Republican said he would be "deeply concerned" if no one was attacking him because "it wouldn’t mean we were winning." He told volunteers that they are terrifying the Washington establishment because he is running his campaign through volunteers, not slick television ads, and that the attacks would ramp up with a ferocity never before seen.

Despite this and Cruz's constant lambasting of the Republican establishment, his political director, Mark Campbell, told supporters that many of their members are breaking for Cruz.

"More and more of the establishment wing of the Republican party is coming to our campaign as the alternative to Mr. Trump," Campbell said. Trump and Cruz have had an odd political bromance, with Cruz drafting behind Trump in an effort to pick up his supporters.

Read: The end of the Trump-Cruz bromance? Not if Cruz has his way.

"We wish Donald Trump a Happy New Year. We hope he had a wonderful holiday season. But all of us believe very firmly that Ted Cruz will be the next president of the United States," Campbell said.