It would be easier to answer this question if we could know what political cartoons you have been shown about foreign policy in the Reagan years. I have provided two cartoons to help with this answer.
In general, political cartoons can only tell us how particular individuals perceived Reagan’s foreign policy. We can assume that many people agree with the opinion of any syndicated cartoonist because otherwise they would not be syndicated. However, we cannot know for sure that any particular cartoon has the agreement of a large portion of the population. Thus, cartoons can only tell us what sorts of issues were important in Reagan’s foreign policy and how certain individuals felt about those issues.
For example, this cartoon can tell us that issues of communism loomed large in Reagan’s foreign policy. It can also show us that this particular cartoonist believed that Reagan was making too much of the communist threat. This is shown by the excessive size of the communist countries that seem to be menacing the free world.
As another example, this cartoon shows us that issues of Iran, the Middle East, and missile defense were all important in the Reagan years. It also implies that Reagan was misguided about some or all of these issues. This is seen most clearly in the tattoo of the person who appears to be Khomeini, labeled as a “moderate.”
Thus, cartoons can show us what issues were important and what certain individuals thought of Reagan’s approaches to those issues.