The Weimar constitution was very easy to manipulate.

After the Reichstag fire, the NSDAP used Article 48 of the constitution to suspend an ass load of constitutionally protected rights, as well as arrest all communist and a few social democratic legislators with the Reichstag Fire Decree. Later, Reichstag president Hermann Göring introduced a technicality* regarding the presence of representatives in order to bypass the quorum requirement when voting on constitutional amendments. The arrest of legislators, the manipulation of quorum rules, and the Reichstag fire itself, helped guarantee the passing of the Enabling Act, which killed the Weimar Republic.

The NSDAP had 33% of the seats on the eve of the fire, and 44% in the elections just 6 days after the fire. Despite not having a majority, the NSDAP exploited weaknesses in the constitution to gain absolute power over the government, outlaw all other parties, and effectively nullify the entire constitution. (After the Enabling Act, the constitution simply provided legitimacy for the Reichstag Fire Decree and the Enabling Act and served no other purpose.)

There were cracks in the foundation. Personally, if all it took was a minority party with a few tricks up their sleeve, the republic's destruction seems almost inevitable.

EDIT: *The Reichstag needed a quorum of two-thirds (2/3 of all members had to be present) before voting on constitutional amendments, and required that 2/3 of all present approve the amendment; there were no other requirements or procedures separating constitutional amendments from regular laws. The SPD wanted to boycott the elections so the quorum would not be met. Göring changed the Tag's procedural rules such that if a member was "absent without cause" they would be declared "present". The SPD decided that boycotting would not work and simply voted against the Enabling Act. With the communists arrested, it didn't work.

EDIT2: Fixed amendment requirements in first edit.

EDIT3: The worst-case scenario of arrests + rule manipulations would have allowed a constitutional amendment to pass with only 4/9 of legislators agreeing--less than half the Reichstag! First, the government can have 1/3 of legislators arrested (like what the NSDAP did to the KPD and a few SPD members), then force the other 2/3 to show up with the rule change (prevent boycotts a la Göring). Then, if only 2/3 of those who show up vote yes, the amendment is passed. Any amendment could have passed with Ayes from only two-thirds of the two-thirds of legislators that are present.

(2/3)*(2/3) = (4/9)

4/9 < 50% of legislators

In one word, no. The Weimar Republic started essentially when the sailors in Kiel mutinied, and the Kaiser had to step down on 9th of November 1918. On that day, the communist Karl Liebknecht declared a socialist republic and at almost the same time the social democrat Philipp Scheidemann declared a republic. The conservative Paul Becker did comment on the next day

The work fought for by our fathers with their precious blood – dismissed by betrayal in the ranks of our own people! Germany, yesterday still undefeated, left to the mercy of our enemies by men carrying the German name, by felony out of our own ranks broken down in guilt and shame. The German Socialists knew that peace was at hand anyway and that it was only about holding out against the enemy for a few days or weeks in order to wrest bearable conditions from them. In this situation they raised the white flag. This is a sin that can never be forgiven and never will be forgiven. This is treason not only against the monarchy and the army but also against the German people themselves who will have to bear the consequences in centuries of decline and of misery.

In the following month the rift between social democrats and communists escalated to violent revolution. So already at the start of the Weimar Republic, the conservatives, that is those who wanted the Emperor back, felt that politicians betrayed the army, and the communists felt that they lost the revolution. In the immediate aftermath there were several attempted coups and revolutions, most famously the beerhall coup. And the situation did not really stabilize until the end of 1923.

Stabilizing is here a rather relative term, the Weimar Republic had seven different coalitions between 1924 and 1929, of which only three had a parliamentary majority. And in 1925 the monarchist Paul von Hindenburg was elected as president. Not to mention that after 1920, the NSDAP and the KPD, which both rejected the parliamentary system, had combined always more than 10% of the seats in the parliament. And the rise of paramilitary wings of the different parties, the SA of the NSDAP, the Reichsbanner of the democratic parties and the Rote Frontkämpferbund of the communists.

In March 1930 the grand coalition between Zentrum and SPD did break apart. And only three days later Hindenburg installed Brüning as the new chancellor, instead of waiting for the end of coalition negotiations. In July Hindenburg dissolved the parliament, after the parliament refused to pass a law proposed by Brüning. In the following elections the NSDAP jumped from 2.6% to 18.3%. And after the election, the SPD backed Brüning under the thread of another dissolution of the parliament, out of fear of further gains for the Nazis.

This continued until 1932, a year with two elections. Neither produced a parliament with a democratic majority, instead the KPD and NSDAP combined held the majority. Hindenburgs newly appointed chancellors, von Papen and von Schleicher, were not able to secure a majority in the parliament or to govern using emergency measures. Finally in late 1932 von Schleicher did offer the chancellorship to Hitler, who abolished democracy in the first half of 1933.

So the Weimar republic was never a fully functioning democracy. In the beginning there was violence, then they elected a monarchist as president and in the end the government relied on the powers of the president, instead of the parliament. Not to mention the problems with the judicial system. For some further reading a report from the Pittsburg Gazette on the situation in Germany in probably late 1931: Pittsburgh Post-Gazette - Jan 15, 1932 - Behind the German smoke screen and in German there is a rather nice overview by the bpb Weimarer Republik.