Opportunism is the conscious policy and practice of taking selfish advantage of circumstances, with little regard for principles.
Most politicians are "opportunists" to some extent at least (they aim to utilize political opportunities to their advantage), but the controversies surrounding the concept concern the exact relationship between "seizing a political opportunity" and the political principles being espoused.
The term "opportunism" is often used in a pejorative sense, mainly because it connotes the abandonment or compromising of political principles, if not formally, then in reality. Thus, the implication is usually that opportunist behavior is unprincipled: political means to achieve an end have become ends in themselves. In that case, the original relationship between means and ends is lost.
In politics, it is sometimes necessary to insist on political principles, while at other times it is necessary to insist on political unity among people who may differ or conflict to a greater or lesser extent in their beliefs or principles.
If political principles were typically defined in an inflexible, non-negotiable, way a likely result would be sectarianism, since few people beyond "true believers" could support a political practice based on such rigid positions. Normally, there must be at least some freedom in how political principles are formulated, interpreted, and actually applied.
Opportunistic behavior may be evident in strategic alliances, in which one party uses the relationship to better their position, often at the expense of the other.
On the other hand, political principles can also be "diluted", reinterpreted or ignored, purely for the sake of promoting a contrived political unity. In consequence, a coherent rationale for being in the same organization is gradually lost.
Thus, political integrity typically demands an appropriate combination of principled positions and political flexibility, so that a morally consistent behavior results. Whereas it may be necessary to seize a political opportunity when it presents itself, it should ideally be seized also with an appropriate motivation, and on a principled basis. Which is basically a leader of an increasingly large group.
But this ideal may be difficult to honor in practice, with the result that opportunistic mistakes are made. Few actions are intrinsically opportunist; they are opportunist in a specific context, or from a specific point of view about means-ends relationships involved. This may make an objective assessment of opportunism difficult.
Typically, opportunist political behavior is criticized for being short-sighted or narrow-minded. That is, in the urge to make short-term political gains or preserve them, the appropriate relationship between the means being used and the overall goals being aimed for is overlooked. The result might well be, that "short term gain" leads to "long term pain".
Some political analysts find the source of opportunism in a specific political methodology that is applied to maintain or increase political influence. An example might be so-called suivisme (a French word for political "tail-ending" or "tailism") where people try to follow and infiltrate any movement that shows signs of being popular. Populism is sometimes regarded as an intrinsically opportunist form of politics, catering to the "lowest common denominator".
Other analysts see opportunism as originating in perceptions of the relative magnitudes of risk associated with different policy alternatives. Here it is argued that the larger a political organization grows and the more influence it has, the less likely it is that it will pursue policies that could potentially result in the loss of the gains it has previously made. It would be more likely that an organization will compromise its principles to some degree, in order to maintain its position, than to continue pursuing its principles regardless of the consequences. Or, at the very least, the greater political influence obtained, the more pressure exists to compromise one's political principles.
To some extent, politics unavoidably involves dilemmas about whether to insist on one's own principles (and risk being isolated) or to adapt to a more widely-held opinion for the sake of working together. Accordingly, most political situations involve some potential for opportunism.
Thus, there may not be any generally applicable rule or technique (a "philosopher's stone") that could be invoked in advance to prevent opportunism. At best, one could be aware of the possibility that opportunism could become a real problem, and take steps to minimize the risk.
Some politicians have argued that opportunist errors are preferable to sectarian errors, to the extent that the opportunist, whatever his "sins" may be interpreted to be, at least remains among majority opinion or "among the masses". But because the majority could be quite wrong in regard to particular issues, adapting to that majority opinion on those issues might, in a specific context, be an even bigger error.
In France, "opportunists" designated moderate Republicans, such as Léon Gambetta, who dominated the Third Republic after the eviction of the monarchists at the end of the 19th century. The term was not inherently critical, but rather reflected pragmatism.