1968 polls do back up the contention to some extent. Here are several we found using iPoll, a comprehensive, up-to-date source for US nationwide public opinion. A full-text retrieval system, the iPOLL online database is organized at the question-level, providing the tools to sift through nearly a half million questions asked on national public opinion surveys.
From iPoll
Gallup Poll (AIPO) (September, 1968)
Do you approve or disapprove of the way the Chicago police dealt with the young people who were registering their protest against the Vietnam war at the time of the (1968) Democratic convention?
56% Approve
31 Disapprove
13 No opinion
~~~~~
Nixon Poll (October, 1968)
Within the past few weeks, has your opinion of Richard Nixon become more favorable or less favorable than it was before?
28% More favorable
16 Less favorable
51 Same as before
5 No opinion
~~~~~
Survey by Richard Nixon. Methodology: Conducted by
Opinion Research Corporation, October 7-October 10,
1968 and based on telephone interviews with a national
adult sample of 980. (USORC.101068.R06)
Data provided by The Roper Center for Public Opinion Research, University of Connecticut.
~~~~~
Gallup Poll (AIPO) (September, 1968)
IF NIXON WERE TO TAKE A STRONGER PEACE POSITION ON VIETNAM WOULD THIS MAKE YOU MORE LIKELY TO VOTE FOR HIM, OR NOT?
35% YES
57 NO
8 DON'T KNOW
Methodology: Conducted by Gallup Organization,September 19-September 24, 1968 and based on personal interviews with a national adult sample of 1,504.
(USGALLUP.768.Q15)
Data provided by The Roper Center for Public Opinion Research, University of Connecticut.
~~~~~
Gallup Poll (AIPO) (September, 1968)
Did you happen to pay any attention at all to the(1968) Democratic convention held in Chicago?
42% Quite a lot
44 Some
14 None
Methodology: Conducted by Gallup Organization,September 1-September 6, 1968 and based on personal interviews with a national adult sample of 1,507.
(USGALLUP.68-767.R01)
Data provided by The Roper Center for Public Opinion Research, University of Connecticut.
~~~~~
Harris Survey (September, 1968)
Reaction to the Democratic Convention. Do you agree or disagree.... Mayor Daley was right the way he used police against demonstrators
66% Agree
20 Disagree
14 Not sure
Methodology: Conducted by Louis Harris & Associates, September 11-September 13, 1968 and based on personal interviews with a national voters sample of 1,324.
(USHARRIS.100368.R2B)
Data provided by The Roper Center for Public Opinion Research, University of Connecticut.
~~~~~
Harris Survey (September, 1968)
Reaction to the Democratic Convention. Do you agree or disagree.... Anti-Vietnam demonstrators had protest rights taken away unlawfully
14% Agree
66 Disagree
20 Not sure
Methodology: Conducted by Louis Harris & Associates, September 11-September 13, 1968 and based on personal interviews with a national voters sample of 1,324.
(USHARRIS.100368.R2F)
Data provided by The Roper Center for Public Opinion Research, University of Connecticut.
~~~~~
Harris Survey (September, 1968)
Reaction to the Democratic Convention. Do you agree or disagree.... Way they ran convention, Democrats proved they couldn't govern America
34% Agree
49 Disagree
17 Not sure
Methodology: Conducted by Louis Harris & Associates, September 11-September 13, 1968 and based on personal interviews with a national voters sample of 1,324.
(USHARRIS.100368.R2D)
Data provided by The Roper Center for Public Opinion Research, University of Connecticut.
