What is the meaning of "v'Nasobu Aleinu"?
Malbim: They will be united [against us].
What is the meaning of "v'Hichrisu Es Shemenu"?
Malbim: We will lose our reputation of being mighty. This will desecrate Your name, which was elevated through us.
What was the question "u'Mah Ta'aseh l'Shimcha"?
Rashi #1, citing a Midrash: Your name is joined with our name! (It is disgraceful for Your name that we were defeated.)
Rashi #2: What will be of the fame of Your strength, which was publicized? Now, people will say that You weakened!
Radak: People will say that You do not have ability [to defeat the Kena'anim]. It is as if Your name was diminished in their eyes!