There is some amount of disagreement on this topic, even within the discipline of political science. My own view is that political science is not a science, but there are many political scientists whose work consists of studies that are driven by data and which utilize such techniques as regression analysis.
Within the discipline of political science, there is something of a split between people who want to do qualitative studies and those who want to do quantitative studies. The former group would be less likely to see political science as a science. They would be more likely to say that it is a field that can never be truly scientific. They would say that political scientists need to do things like case studies in which they closely examine (for example) the actions of a given president to see what sorts of “laws” they can extrapolate from that president’s actions. This is not something that can be done scientifically.
On the other hand, you have the more quantitative people who are interested in crunching numbers. These people are more likely to want to take large sets of data (like votes in Congress) and to try to use statistical methods to determine what measurable factors are driving the ways in which members of Congress vote. They would say that political science should be conducted in this quantitative way.
My own view is that the most interesting questions in political science cannot be answered with numbers. For example, we cannot say what makes a great president through numbers and science. We cannot use science to show what impact the Supreme Court has on movements for rights. We cannot use science to determine whether President Obama would have been better off compromising more (or less) with the Republicans in the House.
Political scientists can and should try to be as scientific as possible in terms of formulating their questions and looking for data that can answer those questions, but they cannot aspire to do experiments or statistical analyses on most of the more interesting issues in the discipline.