The excerpt suggests that pro-slavery Southerners O considered John Brown to be uncharacteristic of

most northerners.

O

were beginning to identify the Republican cause

with fanatic abolitionism.

supported the platform of the Liberty Party.

supported the Northwest Ordinance and

Wilmot Proviso.

O

were beginning to identify the Republican cause  with fanatic abolitionism.

Explanation:

The above is the correct  statement which aided in suggesting that pro-slavery Southerners were beginning to associate the Republicans with a fanatic abolitionism. To them, that singular knowledge was what made them to be careful with the Republicans.