However, a straightforward reading of Rambam, without trying to kvetch it in order to make one's favored Rebbe into a messianic candidate, shows that the Rebbe fulfilled hardly any of the conditions laid out by the Rambam to be bechezkat mashiach. Only be creative reinterpretation can he be said to have fulfilled any of the conditions.
Rambam's paradigm for mashiach was via the natural route, with the difference between now and messianic times being a lack of shibud malchuyot. His paradigm is Bar Kochba.
A straightforward reading of Rambam shows that David Ben Gurion, Israel's first Prime Minister, fulfills many of the conditions without kvetch, while the Rebbe zatza"l did not. Plus, David Ben Gurion's name was David, and the gemara states:
אמר רב עתיד הקדוש ברוך הוא להעמיד להם דוד אחר שנאמר (ירמיהו ל) ועבדו את ה' אלהיהם ואת דוד מלכם אשר אקים להם הקים לא נאמר אלא אקים
Let us go through each stipulation and see who fulfills it better, on a literal level, without kvetching the peshat in the Rambam. I now quote myself, from a comment on that post:
ואם יעמוד מלך מבית דוד, הוגה בתורה ועוסק במצוות כדוד אביו, כפי תורה שבכתב ושבעל פה, ויכוף בה כל ישראל לילך בה ולחזק בדקה, וילחם מלחמות ה' – הרי זה בחזקת שהוא משיח.
Let us parse this:
a) ואם יעמוד מלך מבית דוד. Was the Rebbe a king? Certainly not in the literal sense. If you want to read it as derash, fine, but realize that you are reading it as derash. But the first Prime Minister could certainly be considered a king. I do not know that he knew of any lineage traced back to David HaMelech, to make it mibeis David. In terms of the Lubavitcher Rebbe, I am unsure of all the claims as to the lineage. If through Rashi, then Rashi descends not from Shlomo but of his brother. And Rashi only had daughters, so it would not be ben acher ben.
b) הוגה בתורה ועוסק במצוות כדוד אביו, כפי תורה שבכתב ושבעל פה
This king is supposed to be religious, not like certain kings who were irreligious, or were Sadducees. The Rebbe was religious, but he was not a king. Ben Gurion was not religious, but was a king.
c) ויכוף בה כל ישראל לילך בה ולחזק בדקה
As king, he will see up a theocracy under his monarchy, such that religious law becomes the law, such that everyone is compelled to do it. Again, the paradigm is one of monarchy. Kiruv is nice and all, but this was not the Rambam's conception, al derech hapeshat.
The Rebbe did not fulfill this. But though David ben Gurion was not Orthodox, he did take steps to set Orthodox, Pharisee law, as the law of the land, to an extent:
"He sent a letter to Agudat Israel promising that the Shabbat would be Israel's official day of rest, there would be no civil marriages, and the Orthodox sector would be granted autonomy in the sphere of religious education."
d) וילחם מלחמות ה. This does NOT mean making people religious. This means physically leading people in fighting wars, such as to reconquer eretz yisrael. The fact that Tzivos Hashem is named that is cute, but that is not fighting the wars of Hashem, on a peshat level. We can see that because in the next statement about success, Rambam talks about succeeding in these wars -- ונצח כל האומות שסביביו. Again, David ben Gurion is a much closer candidate than the Rebbe in terms of fulfilling the actions required
e) הרי זה בחזקת שהוא משיח
Such a person is under the presumption of being mashiach, but we are not yet absolutely sure.
So the Rebbe is an extremely *weak* candidate, and least based on the stipulations of the Rambam. I am not saying that David ben Gurion is mashiach, but in terms of fulfilling the stipulations of the Rambam, he is so, so, much closer. Only by kvetching and reading derash into the Rambam can you claim the Rebbe was even bechezkas mashiach. When comparing them side by side, I think the weakness in this reinterpretation is obvious.
But then, people take it a step further:
אם עשה והצליח, ונצח כל האומות שסביביו, ובנה מקדש במקומו
He succeeded at kiruv and helping establish the state of Israel (?), and he built up the mikdash -- 770 -- in its place. This is obviously nonsense.
David ben Gurion did fulfill ונצח כל האומות שסביביו. But he missed out on his opportunity to build the mikdash in its place, leaving the Temple Mount in Muslim hands, stating "The Western Wall is for the Jews at the moment, and the Temple Mount is for the Muslims at the moment, and that is the reality we have to accept."
וקבץ נדחי ישראל –
g) The Rebbe helped bring in Russian Jewry.
But looking again at Ben Gurion, just for comparison:
"In 1948, as head of the provisional government, David Ben-Gurion proclaimed the establishment of the State of Israel and the beginning of the "ingathering of the exiles""
"In the first five years of statehood, Ben-Gurion's forceful and charismatic leadership as Prime Minister led to waves of mass immigration which doubled the country's population. He directed absorption endeavors, investing the majority of the new nation's limited resources in integrating the immigrants; secured outlying areas by building settlements on the periphery; and instituted universal education in a non-partisan public school system."
Such a person is (continuing Rambam):
הרי זה משיח בוודאי, (ויתקן את העולם כולו לעבוד את ה' ביחד, שנאמר: "כי אז אהפוך אל עמים שפה ברורה לקרוא כולם בשם ה' ולעבדו שכם אחד") (צפניה ג,ט):
But the kvetches of mashiach bevadai only follow from a midrashic reading of Rambam, which Rambam never intended.