With fewer than six months to go until the German general election, Martin Schulz has piled on the pressure to Angela Merkel with three different but consecutive polls placing the top two parties neck and neck.

Merkel's conservative Christian Democratic Union (CDU) and Martin Schulz's centre-left Social Democratic Party (SPD) are tied in the polls as a series of important state elections approach in the coming months.

The SPD trailed its grand coalition partner for much of the past decade, but since Schulz took the helm of the party in January, it has had a renaissance which it is trying to capitalise on.

Three polls carried out between the 20 and 27 March by INSA, Civey and Infratest found no difference in support for the two parties.

Who is Martin Schulz?

Schulz is regarded as the ultimate Brussels insider, and has managed to maintain a distance from the day-to-day squabbles of German domestic politics, perhaps contributing to his popularity.

First elected to the European Parliament in 1994, he quickly rose to lead the Social Democrat group, the Progressive Alliance of Socialists and Democrats.

In 2003 he was involved in a memorable spat with then Italian Prime Minister Silvio Berlusconi, who responded to criticism by likening Schulz to a Nazi concentration camp guard.

In 2012, he was elected European Parliament president, and was re-elected for a second term in 2014. However, opposition to his continued leadership by a the parliament's conservatives has led to him re-entering German politics.

Despite seeking to increase the involvement of MEPs in decision making during his term as European Parliament president, he faced criticism for his reliance on the backroom deal-making that has dented the credibility of the EU.

CDU bouncing back?

Despite the tight polls and a resurgent SPD, Merkel's party has maintained an edge especially after a regional election in the state of Saarland on Sunday (26 March), which saw the CDU improve more than expected on the 2012 result.

The result came as a surprise to the SPD, but is a precursor to two major votes in the next few months.

Saarland with a population of about one million people is comparatively small compared to the almost three million who live in the country's northernmost state of Schleswig-Holstein who go to the polls on the 7 May.

But the biggest challenge will be the western state of North-Rhine-Westphalia which has more than 17 million inhabitants and on the 14 May will be viewed as a test run for the general election.

Since then a new poll by Forsa found that if the chancellor was directly elected then 41% would back Merkel while 34% would vote for Schulz, leading to concern within the SPD that the Schulz bump may be over.

Schulz, who was the president of the European Parliament between 2012 and 2017, is hoping to take the SPD back into power after years either in opposition or as a junior coaltion partner with the CDU.

Merkel, on the other hand, has been chancellor since 2005 and is aiming to win a fourth term on the 24 September.