Ukrainska Pravda published an analysis of Viktor Yushchenko's decline in popularity (link is to the Google translate version; the original is here) focusing on critical events over the last five years. The UP article draws from the Razumkov Center's polling and analysis. and uses responses to the question: "Do you trust the work of Viktor Yushchenko?" that has been tracked since 2002. Respondents were presented with three options: "fully support," "support individual actions," "do not support," in addition to "do not know [his work]," and "hard to say." The UP assessment focused only on the first response - "fully support" - and traced the dynamics of responses over time.
It may be more useful to look not at full support, but rather both flavors of support together. The graph below presents full and partial support combined (blue), along with dissatisfaction (orange). While the trends that UP points out generally persist, the intensity of change differs. For example, the change in attitudes about Yushchenko reflected in the June-October 2008 results are a small downward blip in the UP article; the decline is more precipitous with full and partial support added together. The increase in "no support" rises to 75.6% of respondents from June-October 2008 - an increase of 20 percentage points from the June 2008 poll. The financial crisis and President Yushchenko's failed bid to hold another early parliamentary election loom large over that period, and could constitute explanatory factors.
More than 50% of respondents trusted Yushchenko in almost all periods prior to and during the Orange Revolution. Since early 2008, trust has dissipated to only 19% in the October 2009 poll. No realistic scenario predicts Yushchenko's re-election. However, rumors have circulated of an agreement between Yushchenko and Yanukovych in which Yushchenko would be nominated for the post of prime minister (as well as receive some policy concessions) in exchange for help challenging Tymoshenko. Yushchenko's lack of popularity suggests that if the agreement were real, Yanukovych has a strong incentive to renege on his end of the bargain. While Yanukovych might benefit from a non-aggression deal with Yushchenko, and perhaps gain support from Yushchenko's administrative resources, Yanukovych gains little from nominating such an unpopular politician to be prime minister.
Moreover, since parliament gained more authority over the appointment of the prime minister after constitutional reforms took effect in 2006, it is not clear that Yushchenko could bring along enough deputies to scuttle the current coalition government and hand over the reins to Yanukovych.