Arduino attachment to breadboard

Is it safe to push an Arduino into a breadboard.

It feels like the pins will bend.

What "arduino" can plug into a breadboard? Please show us what you are taking about??

Most of them don't plug into a breadboard. A Nano, Micro, Teensy and some other variants will plug in to a breadboard.

Maybe a bigger hammer?

The Pro-mini fits just fine, and basically any micro-controller with downward facing pins are breadboard friendly. It's just a lot of pins to push in.

Assuming you have a Nano or similar, first, use a piece of 22 gauge solid wire stripped about 1/2 inch (12 mm) to punch every hole on a new breadboard to make sure they are clear of mold flashing, (especially the cheapies), after that, turn the breadboard upside down and tap firmly on a flat, hard surface to make sure all the holes are clear of "trash", then place the Nano pins in the holes and "rock" it down pressing firmly on one end till the pins are in about 2 mm, hold that end and, with the other hand, press the other end down about 3 mm keeping it level side to side, alternate end to end 'til it's full down. If it takes more than about 3 or 4 pounds (2 kg) of force, stop and make sure all holes are clear and no pins are bent.