Very Weak Key, but Strong Conflicts that get Agreed on when the root changes.

C
Guitars are more Obvious, but vocals are doing C and F (P4) back n' forth with a pretty big Conflict. C is repeated ,but the 4 is strong already, is on (4)&, and is longer and louder.

G
345 1 3 4 5 is more Agreeing. The D is slightly longer and on the (4)&, but it's less conflict than we had on C. There's also the memory of the F note (TT issue), but the 3 has a 1/2 step move out.
In the second section on G we have complete repetition of the 345 1 phrase which is more Ambiguous than the previous phrase.

D
43 then the bass puts in a 2 1 b7 5 4 b3(and 3 2 1 6 5 4 to Key), which does make the Key more obvious by putting the TT issue (3 b7) on the D root first, and also getting a half step out of the TT with b3. The 3 of D was already in the melody so having a b3 afterwards is a crushing blow.

C
We do have a 4 1 which is risky, but now that F note was the b3 that was hurt on D. We also have the memory of starting on C. Can't say that this was a stronger move than the others though.

Good example of a song that maybe only has roots or alternating keys.