This issue isn't as simple as the Republicans would like it to be...
The fact is that Zeleya wasn't trying to extend his term in office. Zeleya was trying to establish a "National Constituent Assembly". This assembly would have allowed labor groups, farmers and civil organizations to have a say in a political system that is controlled by wealthy. And, the establishment of the "NCA" had strong support within these groups, as-well-as in the population in general...
Honduras media is controlled exclusively by the same wealthy entities as is the political system, so anti Zeleya propaganda was commonplace, and the political pressure to oppose his NCA poll, that would have given Hondurans the ability to rewrite there own constitution, was overwhelming amongst the ruling factions in Honduras...
What Zeleya was trying to accomplish wasn't "unconstitutional". The NCA was an initiative that could have undermined the control that the wealthy ruling class in Honduras has enjoyed for decades, so it was extremely unpopular within Honduran leadership...
And, since Zelaya's actions were not illegal. And, given the fact that the NCA wouldn't have even been established until after the election that would have constitutionally ended his presidency, thus making it impossible for him to "extend his presidential term", (as were the accusations that led to his expatriation), Zeleya's removal from office and subsequent expatriation were by definition, a coup. And, "the coup" itself was unconstitutional, because the Honduran Constitution prohibits the handing over or expatriation of Honduran citizens...
So, in the end, Obama is supporting the illegally ousted Honduran President, and this group of "rogue" Republican US Senators are undermining US relations in the region by supporting the illegal Honduran government (that gained control by force) through acknowledging them openly against the wishes of the acting US President...
But, it's not really that surprising, Republicans aligning themselves with wealthy illegitimate foreign regimes; business as usual...