Jeb: Unlike Trump, I've always been loyal to GOP
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After Trump posted a tweet touting his pledge not to make a third-party run, Bush replied by including a photo with his own signature under text reading, "Voted Republican since 1972."
The barb is part of a continued push from Bush's campaign to point out that Trump has previously been registered as a Democrat and donated to Democrats. 
“He was a Democrat longer than he was a Republican,” Bush said at a New Hampshire town hall last month. “He’s given more money to Democrats than Republicans.”
The former Florida governor made similar remarks in Spanish at an event in Miami on Tuesday.
“He’s not a conservative. That’s my point,” Bush told a crowd in Spanish at La Progresiva Presbyterian School.
Trump replied that Bush should “set the example by speaking English while in the United States.”
Bush has also gone after Trump for his previous support of liberal policies such as a tax on assets and a single-payer healthcare system.
Other candidates who have come out strongly against Trump, such as Sen. Rand Paul (R-Ky.), have also accused him of being a "fake conservative" and aiding Democrats. 
In signing the Republican National Committee pledge on Thursday, Trump signaled that he plans to support the eventual Republican nominee, ending a months-long drama.
“We will go out and we will fight hard and we will win, and most importantly we will make our country great again, because that’s what it’s all about," Trump said. 
- Bradford Richardson contributed
- Updated at 4:08 p.m.