Berlin (CNN) Angela Merkel may have been hoping for a smooth exit to her long tenure as German Chancellor. Instead, she could be in for a rough ride, after suffering two major political blows in the past week.

First, her chosen successor as Germany's leader, Annegret Kramp-Karrenbauer -- better known as AKK -- has plunged in the polls after a series of blunders.

Second, Merkel's coalition partner, Andrea Nahles of the Social Democrats, resigned after taking a battering in last week's European elections.

On Sunday, Merkel made a statement at her party headquarters in which she vowed to carry on and keep the coalition together.

"We will continue the government's work with all seriousness, and above all greatly conscious of our responsibility," she said. "The issues we must solve are plain — in Germany, in Europe and in the rest of the world."

Understanding GroKo

To get Merkel's predicament, you have to understand "GroKo" -- the German nickname for the Grand Coalition between the two largest parties in the Bundestag -- which for most of Merkel's time in office has been between her conservative Christian Democratic Union party (CDU) and the center-left Social Democrats, or SPD.

The SPD have been stalwart partners to the Chancellor for her first, third and now fourth term in office (though she had a brief dalliance with the Free Democrats during her second term), consolidating Merkel's control over Germany's parliament.

But over the years, and particularly after the 2015 refugee crisis, voters became disenchanted with GroKo. In the 2017 federal elections, millions deserted the CDU and SPD for the far-right, anti-immigration Alternative for Germany (AfD), and the German Greens, who are now ascendant on the left.

Despite the dismal results, Merkel was not ousted and her CDU clung to power with the help of its coalition with the SPD, despite objections from the SPD's radical youth wing, who argued that the coalition with the CDU would kill their party.

EU election fallout

The results of the EU election last week prove that the SPD's internal critics were right: the party plummeted to just 15% of the vote in Germany, a historic low.

Adding insult to injury, in a regional election held the same day, it lost the top spot in Bremen, a city the SPD has held for more than 70 years.

That prompted SPD leader Andrea Nahles to resign, and triggered calls by party members to finally pull the plug on the coalition, which would likely imperil Merkel's last term in power.

"The discussions within the parliamentary group and the large amount of feedback from the party have shown me that there is no longer support for me in holding these offices," Nahles wrote in an email to party members on Sunday, urging continuing support for the Grand Coalition.

The fall of the SPD, and the possible collapse of the coalition, would have been bad enough for Merkel. But it was compounded by a series of political blunders from her appointed CDU successor, Annegret Kramp-Karrenbauer.

The European Election was the first test of AKK's vote-getting ability without having Merkel to help her out. While Merkel remains Chancellor until 2021, she is no longer head of the CDU and has conspicuously left the campaigning to AKK. It did not go well.

Just before EU voting day, she had an online dust-up with a group of YouTubers, who had urged voters not to elect the CDU, SPD or AfD.

Kramp-Karrenbauer called their YouTube videos political "propaganda" that needed to be regulated, unleashing a social-media backlash against the CDU.

The politician admitted that she had failed to connect with voters. The EU election results showed that the CDU had lost more than a million votes at the ballot box, many of them to the Greens. That was a shock for CDU members who may have hoped a fresh leader would put a halt to the party's slide.

All of which has fueled reports of Merkel herself casting doubts over whether her heir apparent is up to the job. Bloomberg, citing two officials close to the Chancellor, reported that she had "given up hope" in her successor. Merkel dismissed the report, calling it "nonsense."

In the meantime, Kramp-Karrenbauer doesn't appear to be instilling confidence either inside or outside the party.

Last week a Forsa poll by CNN affiliate RTL showed that 70% of respondents did not want Kramp-Karrenbauer to take over for Merkel as Chancellor.

Merkel (R) with Kramp-Karrenbauer at CDU headquarters in October.

Rise of the Greens

What does that mean for Merkel? Well, she's not out just yet. GroKo still stands and her term as Chancellor doesn't end until 2021.

But if the coalition finally does crack, the CDU will need to build another coalition, this time with the Free Democrats and the Green party, now surging in the polls.

For the first time ever, this week the Greens polled in first place, usurping the CDU, according to the Forsa Trendbarometer conducted by CNN affiliate, RTL.

Merkel is nothing if not a pragmatic dealmaker. But she has tried this political combination before and failed. In the past, Merkel has said she only intends to complete her term and ruled out running for any political office after 2021. Is her successor ready to take on the challenge?

On Monday, when asked if she was prepared to become chancellor in the event of a coalition collapse, Kramp-Karrenbauer took it in her stride.

She said: "There are very good reasons to not recklessly end a government, considering the situation in Germany and Europe. We at the CDU are obliged to provide reliability and stability."

"You can be assured that the CDU is ready for any possibility that may or may not happen."