The answer is yes according to Jim Marrs in his book Crossfire: The Plot That Killed Kennedy (1989):
"President Kennedy rode right into the middle of (an ambush) in an open limousine that violated security regulations by making a 120-degree turn in front of the Texas School Book Depository."
Security regulations had already been violated in making the 1st turn. When security is compromised (slowing down, stopping, turning) then additional protective measures were to be used.*
*Agents riding on running boards of the President's car, having additional security in the crowds, making sure windows of buildings are secured.
There is no evidence to suggest any of these additional security actions were taken after the motorcade turned onto Houston Street.
Why were these turns were made in the first place?
The Warren Report (1964) said it was "impossible" to access the Stemmons Freeway by way of Main Street.
"The Elm Street approach to the Stemmons Freeway is necessary in order to avoid the traffic hazards which would otherwise exist if right turns were permitted from both Main & Elm into the freeway.
To create this traffic pattern, a concrete barrier between Main and Elm Streets presents an obstacle to a right turn from Main across Elm to the access road to Stemmons Freeway and the Dallas-Fort Worth Turnpike."
While this may be true for normal circumstances in 1963, this was the President & if his security was top priority, it should have been simple for the Secret Service to have a temporary ramp placed over the concrete barrier or to have a part of the barrier removed.
If this had been done, the motorcade could have proceeded through the Main-Houston intersection & avoided the turns altogether.
The official answer is it was either "impossible" or at best "impracticable" to reach the freeway by staying on Main Street so the turns were necessary.
In the "conspiracy" view, JFK was brought into the "killing zone" by making these turns.