frodo was both the weakest and strongest person in the Trilogy?

[littlemanpoet]

On Sam's stupidity:
In The Passage of the Marshes, just after Gollum's split personality episode over the sleeping Frodo, Tolkien writes:

To [Sam's] simple mind ordinary hunger, the desire to eat hobbits, had seemed the chief danger in Gollum. He realized now that it was not so: Gollum was feeling the terrible call of the Ring.

And in The Black Gate is Closed JRRT writes:

While these doubts were passing through Sam's slow but shrewd mind...

The doubts referred to are Sam's ruminations about Gollum's motivations for leading them away from the Black Gate to 'another' way into Mordor.

Regarding the effect of the Ring on the triad:

Tolkien writes a rather detailed description of the Ring's effect on Frodo and Gollum, as well as Sam's usually accurate perceptiveness. The passage is too long to quote but comes just after the Nazgul pass overhead three times and totally unnerve Gollum (my book, TTT p237-238). It helps to read Frodo's trials from this point to Mount Doom with this description firmly in mind, of

The Eye: that horrible growing sense of a hostile will that strove with great power to pierce all shadows of cloud, and earth, and flesh, and to see you: to pin you under its deadly gaze, naked, immovable. So thin, so frail and thin, the veils were become that still warded it off.

That's Frodo's plight moment by moment.
Of Gollum it says:

Gollum probably felt something of the same sort. But what went on in his wretched heart between the pressure of the Eye, and the lust of the Ring that was so near, and his grovelling promise (italics mine) made in fear of cold iron, the hobbits did not guess.

Here we have the best glimpse of the inner struggle of Gollum, pulled in three different directions at once.