The first phase is 1989-1993. The initial problem is that nuclear experts had never known of any kind of nuclear energy that did not produce commensurate levels of dangerous radioactive emissions. Few people at this time were aware of weak interactions, let alone the possibility that weak interactions could lead to high reaction rates. So, for most scientists, the claimed results were inexplicable according to what they knew at the time.Here is a presentation from SPAWR that gives a more technical view of developments in LENR:
Nuclear physicists couldn't conceive of a way that deuterons could penetrate or overcome the Coulomb barrier at room temperature. Some people, like Hagelstein, tried to come up with explanations for this, but they all relied on imaginary physics.
From the experimental side, the field suffered early on from "experimenter's regress," which is explained by author Harry Collins: "When the normal criterion - successful outcome - is not available, scientists disagree about which experiments are competently done."
When the field emerged in 1989, there was a lot of initial opposition. Many people in science academia responded to it unprofessionally and with outright hostility. Some of these opponents lacked the courage to consider something so radically new and potentially disruptive; some lacked imagination. On a psychological level, it threatened their fundamental understanding of physics. On a practical level, it threatened their stature and funding. It threatened to make their textbooks and coursework obsolete. There were also some other opponents who were researchers who attempted to replicate the initial claim but failed and then may have felt embarrassed and frustrated and then became angry.
The second phase is 1993-2004. During this period, the field was largely neglected by mainstream science and mainstream media. To a great degree, although the researchers would certainly have liked to receive more financial support, I think they were happy to be left alone. However, significant misinformation which occurred from the onset of the field was never corrected in the broader public awareness [during this time]. But that started changing as of [the publication of] Charles Beaudette's Excess Heat & Why Cold Fusion Research Prevailed in 2000 and Steven B. Krivit and Nadine Winocur's The Rebirth of Cold Fusion in 2004. These books began to help correct some of the historical record.
The third phase starts in 2005, when Widom and Larsen came out with their theory, and has continued to the present. During this phase, the field has been experiencing bitter factionalism between two groups. One group is people who maintain their belief in "cold fusion" or, if not [in name], at least the idea of deuterons somehow overcoming the Coulomb barrier. Sometimes, they seem to have loyalty only to the name of "cold fusion." [Often, many of these proponents defend either the concept or the term "cold fusion," much like adherents to a religion defend their right to their beliefs.]
The other group of people, whom you don't hear much about, recognizes low-energy nuclear reactions as real, but they don't presume or assert that it’s a fusion mechanism.
Follow developments of LENR at Steven Krivits NewEnergyTimes blog.