Armin Laschet wracked his brain for an example of how Mrs Merkel had clearly shown more prowess than he possessed throughout her 16-year tenure. But the CDU leader was lost for words and after a long pause eventually muttered: “I don’t know.”
The grim assessment of Mrs Merkel’s ability to lead Germany was offered just two months before she is due to step down before the September federal elections.
In their annual summer interviews of political party leaders, German broadcaster ARD sat down with Mr Laschet to discuss his ambitions and stance on a range of hot topics.
He had a lot to say about his passion for tackling climate change, a potential coalition with the Greens and the sometimes nasty nature of politics.
But when pressed for his view on Mrs Merkel’s strongest points, he lost momentum.
Asked what Mrs Merkel could do better than him, the Chancellor candidate paused for reflection before concluding: “I don’t know.”
He was also quizzed on why he thought people are constantly underestimating him.
He admitted: “I never thought about that.”
But in order to avoid any trace of superiority, he added with obvious satisfaction: “In any case, many have miscalculated in recent years.”
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And he said the global community is in “urgent need” of “major international efforts” to combat the effects of climate change.
Mr Laschet also said he plans to run a fair campaign ahead of the September elections, adding: “That’s my style, I’ll stick to it.”
The Bundestag elections will be held on September 26.
A recent poll showed support for the Greens fell for a third consecutive week.
The research carried out by Insa put the CDU-led bloc on 28 percent and the Greens on 17 percent.
This put the environmentalists on par with the Social Democrats, Mrs Merkel’s junior coalition partner for the last eight years.
The Greens have put forward the only female candidate in the race to replace Mrs Merkel, with Annalena Baerbock vying for the top spot.
The poll was carried out from July 5 to 9 and saw 1,352 people respond.
Meanwhile, Mrs Merkel is busy wrapping up her foreign trips as she prepares to bow out in a matter of weeks.
Earlier this month she enjoyed her final trip to the UK as German Chancellor where she met Boris Johnson at Chequers and sat down with the Queen at Windsor Castle.
This week she will fly to the United States for a meeting with President Biden.
The two countries may come closer to resolving their differences over Nord Stream 2, the pipeline which brings Russian gas to Europe.
Speaking ahead of her meeting with Mr Biden on Thursday, Mrs Merkel said she was unsure of whether she would reach an agreement.
She told reporters: “I think rather not.”
Additional reporting by Monika Pallenberg.