Associated Press/John Minchillo
In this April 18, 2016 file photo, Republican presidential candidate Donald Trump speaks during a campaign stop in Buffalo, N.Y.
Trump is calling out Kasich for only winning one state contest out of 38 in the primary season, referring to the Ohio governor as "1 for 38 Kasich" in tweets Monday morning.
"Lyin' Ted Cruz and 1 for 38 Kasich are unable to beat me on their own so they have to team up (collusion) in a two on one," Trump tweeted on Monday. "Shows weakness!"
He repeated the statistic in a subsequent tweet: "Shows how weak and desperate Lyin' Ted is when he has to team up with a guy who openly can't stand him and is only 1 win and 38 losses."
In a statement Trump released early Monday morning after Kasich and Cruz announced their alliance, Trump emphasized Kasich's losing record while blasting both of them for aligning against him.
"Governor Kasich, who has only won 1 state out of 41, in other words, he is 1 for 41 and he is not even doing as well as other candidates who could have stubbornly stayed in the race like him but chose not to do so," Trump said in the statement, noting that Florida Sen. Marco Rubio, who suspended his campaign last month, has more delegates than Kasich. (The 41 number in this statement also accounts for other contests.)
So far, Kasich has won only his home state of Ohio. But he and Cruz plan to divvy up at least three of the remaining nominating states to try to keep Trump from picking up the 1,237 delegates needed to secure the Republican presidential nomination. The two will cede ground to each other in the states to consolidate anti-Trump support.
An overwhelming victory in the New York primary last week helped Trump move closer to winning the 1,237 delegates needed to secure the GOP nomination on the first ballot during the Republican national convention in July.
While Kasich has been openly positioning himself for a contested convention, Cruz has only recently begun publicly acknowledging that he will not be able to secure the delegates needed to clinch the nomination outright.
Maxwell Tani contributed to this report.