Mr. Freeman's comment on the death of the Republic is less than papal.

According to Charles Freeman, “In the third and early second centuries it had maintained an aura of competence and stability and although its legal powers were limited it had dominated the decision making process.”1 For a long time the senate’s authority was respected. As Freeman states, “Unfortunately the senate’s aura was easily dissipated through its own incompetence and political clumsiness.” 

If this was true, then why did Rome go to war with Carthage in the first place?  It went to war haphazardly and piecemeal fashion.  Why did it suffer so many set backs when at the brink of victory?  This is not a decision of a competent or stable body.  

Secondly, if it was such a stable and competent body, then why did it not assess, anticipate and dispose of Hannibal, Field Marshal of Carthage?

The Senate is like any other legislature stacked full of incompetent and unstable people.  Further, democratic governments like the Republic are by their very nature fraught with instability.  One man governs the will of many in a kingdom.  In a Republic, men are made to govern themselves.  The tales told by Livy are ones were the Romans teetered back and forth between peace and revolution even as the Volscians encamped at the gate.

The reason why the Roman Republic fell is as simple and as straightforward as there are 60 second in a minute and 24 hours in a day.  Men just did not care for the Republic anymore.  They surrendered the only vehicle that secured their liberty for a bit of bread, a bribe, an Alban Villa, and the applause of an up and coming politician.  

Do you think the men of like Cincinnatus would have resorted to Milo  in dealing with Clodius?  How would Camillus dealt with Caesar or Gracchus?  Cicero and Cato tried to tame the beasts of their time.  They prevailed on Pompey and Cicero almost succeeded in co-opting Caesar.  The Liberators won their early battles against Antony.  For every angling tyrant like Octavian and Lepidus, men devoid of self control like Dolabella, Caitline and Curio that might have made the difference in preserving the Republic, but whose moment had come and gone because they could not see clear.  They had chosen to pursue foolish things.

2 Because the empire became so large and because of rising social tensions at home, there were challenges which the senate was unable to meet.
This statement is stupid.  The Rome expanded its territory exponentially when it was a Republic and only gradually and then lost territory exponentially in a monarchy.  Freeman has it wrong.
   The senate also did not have a monopoly on power, as other men were becoming powerful. For instance, when Pompey rose to power and acquired a command, this caused the senate’s power to be lessened and made impotent. 

Other men became powerful in Rome, because of what?  There were always powerful men in Rome since its founding.  For 727 years, Cicero's words "Cedant togae arma"  was a way of life for the Romans.  Force of arms, violence, the willingness to fight brother against brother - that spirit backed the strong men that came of age in the time of Caesar and those men Pompey, Caesar, and Crassus had predecessors in Gracchus,  Saturninus, Sulpicious, Cinna and Fimbria.

What fate does a man of honor have when he is surrounded by knaves?  Ask Cato.  Ask Cicero, Labienus, and Quintus Caecilius Metellus Pius Scipio Nasica.  Ask Brutus why the Republic fell.

It remained for awhile because it had been so powerful. Even when Pompey had power to overthrow the senatorial government, he did not do so. 

Marius financed his legions.  You cannot overthrow a government without perverting the morals of the Army.  When the Army pledges its loyalty to men and not the state, then we have a nation of men and not laws.  This is how the Republic DIED!!!