Chancellor Angela Merkel maintained a clear lead over her Social Democratic (SPD) challengers in opinion polls published today, seemingly impervious to setbacks in state contests four weeks before Germany's general election, according to dpa. The latest opinion polls, commissioned by German ARD and ZDF state broadcasters, showed 35-37 per cent supported Merkel's Christian Democrats (CDU) and their Bavarian CSU sister party, while the SPD languished at 23 per cent. Disappointing CDU results in three of Germany's 16 states last Sunday failed to dent the party's nationwide popularity, which has remained constant throughout the summer months. The SPD's approval ratings have similarly refused to budge from the low 20s, despite repeated attempts by chancellor candidate Frank-Walter Steinmeier to shake up a lacklustre election campaign. However, last Sunday's success story for the Left Party did appear to be echoed in the nationwide surveys. Both ARD and ZDF recorded a 1-per-cent increase for the party, to 11 and 10 per cent respectively. The Left Party, rooted in former East Germany's communist state party, shot from obscurity to 21.3 per cent in Saarland, an unprecedented result to the west of Germany's former divide. The party's rise, under the stewardship of former SPD frontman Oscar Lafontaine, has intensified debate over whether the SPD should consider joining forces with the Left at national level. Of those questioned on behalf of ARD, 56 per cent said they opposed a so-called red-red alliance. However, 49 per cent expected the SPD to enter a coalition with the Left, if the option presented itself after the polls on September 27. Greens and Free Democrats (FDP) saw minor changes in their popularity ratings. The ARD survey gave the Greens a static 13 per cent, compared to 11 per cent (minus 1 per cent) in the ZDF results. The liberal FDP scored 14 per cent (minus 1 per cent) and 15 per cent (plus 1 per cent) respectively.