[3] Reelected in 2005, Sonnenschein's political career survived the dramatic decline of the MNR – hit hard by the stigma of its role in the 2003 gas conflict, the party saw its worst electoral showing in its organizational history.

[12] As with many parliamentarians who hail from the northeastern departments, Sonnenschein's legislative tenure showed more interest in fortifying his local presence, popularity, and influence back home than in dealing with the various congressional conflicts and crises taking place in La Paz at any given time.

[14] In all, according to Movement for Socialism deputy Martín Mollo, Sonnenschein missed ninety-eight percent of all sessions held during the 2006–2010 congressional term, leaving his legislative record largely a mystery and making him a true unknown among journalists and staffers in parliament.

[15] Weakened and in continuous political decline, the MNR entered the 2009 elections on its last legs; its presidential candidate, Germán Antelo, stayed in the race for just over a month, only to abruptly step down to support National Convergence (PPB-CN), the multi-front mega-coalition backing Manfred Reyes Villa.

[22] Amid the conspicuous absence of key party figures and political families from the electoral arena,[23] Sonnenschein was among the few MNR legislators to successfully secure a candidacy on one of the still-competing parliamentary lists – nominated by CN to contest a seat in the Senate,[24] a position he won.

[15] In contrast to the rest of CN's parliamentary caucus – eternally engulfed in constant infighting over the scant positions of power afforded to the minority bloc – Sonnenschein preferred to play a more laid-back role throughout his senatorial tenure, as he had done in the two previous legislatures.